Misplaced Pages

#469530

122-648: The Harvard Bridge (also known locally as the MIT Bridge , the Massachusetts Avenue Bridge , and the "Mass. Ave." Bridge ) is a steel haunched girder bridge carrying Massachusetts Avenue ( Route 2A ) over the Charles River and connecting Back Bay , Boston with Cambridge, Massachusetts . It is the longest bridge over the Charles River at 2,164.8 feet (387.72  sm ; 659.82  m ). After years of disagreement between

244-461: A is the secondary compression index t is the length of time after consolidation considered t 95 is the length of time for achieving 95% consolidation Coefficient of compressibility a v = Δ e Δ σ ′ {\displaystyle a_{v}={\frac {\Delta e}{\Delta \sigma _{'}}}} . The compressibility of saturated specimens of clay minerals increases in

366-412: A BOS process is manufactured in one-twelfth the time. Today, electric arc furnaces (EAF) are a common method of reprocessing scrap metal to create new steel. They can also be used for converting pig iron to steel, but they use a lot of electrical energy (about 440 kWh per metric ton), and are thus generally only economical when there is a plentiful supply of cheap electricity. The steel industry

488-531: A brittle alloy commonly called pig iron . Alloy steel is steel to which other alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include: manganese , nickel , chromium , molybdenum , boron , titanium , vanadium , tungsten , cobalt , and niobium . Additional elements, most frequently considered undesirable, are also important in steel: phosphorus , sulphur , silicon , and traces of oxygen , nitrogen , and copper . Plain carbon-iron alloys with

610-713: A carbon-intermediate steel by the 1st century AD. There is evidence that carbon steel was made in Western Tanzania by the ancestors of the Haya people as early as 2,000 years ago by a complex process of "pre-heating" allowing temperatures inside a furnace to reach 1300 to 1400 °C. Evidence of the earliest production of high carbon steel in South Asia is found in Kodumanal in Tamil Nadu ,

732-540: A change in applied pressure. This broader definition encompasses the overall concept of soil compaction , subsidence , and heave . Some types of soil, mainly those rich in organic matter , show significant creep , whereby the soil changes volume slowly at constant effective stress over a longer time-scale than consolidation due to the diffusion of water. To distinguish between the two mechanisms, "primary consolidation" refers to consolidation due to dissipation of excess water pressure, while "secondary consolidation" refers to

854-444: A change of volume. In this case, expansion occurs. Internal stresses from this expansion generally take the form of compression on the crystals of martensite and tension on the remaining ferrite, with a fair amount of shear on both constituents. If quenching is done improperly, the internal stresses can cause a part to shatter as it cools. At the very least, they cause internal work hardening and other microscopic imperfections. It

976-428: A ferrite BCC crystal form, but at higher carbon content it takes a body-centred tetragonal (BCT) structure. There is no thermal activation energy for the transformation from austenite to martensite. There is no compositional change so the atoms generally retain their same neighbours. Martensite has a lower density (it expands during the cooling) than does austenite, so that the transformation between them results in

1098-583: A hard oxide forms on the metal surface; this is known as stainless steel . Tungsten slows the formation of cementite , keeping carbon in the iron matrix and allowing martensite to preferentially form at slower quench rates, resulting in high-speed steel . The addition of lead and sulphur decrease grain size, thereby making the steel easier to turn , but also more brittle and prone to corrosion. Such alloys are nevertheless frequently used for components such as nuts, bolts, and washers in applications where toughness and corrosion resistance are not paramount. For

1220-445: A hard but brittle martensitic structure. The steel is then tempered, which is just a specialized type of annealing, to reduce brittleness. In this application the annealing (tempering) process transforms some of the martensite into cementite, or spheroidite and hence it reduces the internal stresses and defects. The result is a more ductile and fracture-resistant steel. When iron is smelted from its ore, it contains more carbon than

1342-434: A higher than 2.1% carbon content are known as cast iron . With modern steelmaking techniques such as powder metal forming, it is possible to make very high-carbon (and other alloy material) steels, but such are not common. Cast iron is not malleable even when hot, but it can be formed by casting as it has a lower melting point than steel and good castability properties. Certain compositions of cast iron, while retaining

SECTION 10

#1732772046470

1464-520: A logarithmic relationship is assumed between the volume of the soil sample and the effective stress carried by the soil particles. The constant of proportionality (change in void ratio per order of magnitude change in effective stress) is known as the compression index, given the symbol λ {\displaystyle \lambda } when calculated in natural logarithm and C C {\displaystyle C_{C}} when calculated in base-10 logarithm. This can be expressed in

1586-412: A narrow range of concentrations of mixtures of carbon and iron that make steel, several different metallurgical structures, with very different properties can form. Understanding such properties is essential to making quality steel. At room temperature , the most stable form of pure iron is the body-centred cubic (BCC) structure called alpha iron or α-iron. It is a fairly soft metal that can dissolve only

1708-507: A separated bicycle lane pilot on the Harvard by placing cones to create two wide bicycle lanes. This reduced general purpose lanes from four to two over the bridge. Despite some hiccups involving vandalism, the pilot was deemed a success in the Fall 2022. MassDOT went on to hire Toole Design Group to engineer flex-post separated bicycle lanes, bus priority lanes, and new traffic signal phasing for

1830-534: A small concentration of carbon, no more than 0.005% at 0 °C (32 °F) and 0.021 wt% at 723 °C (1,333 °F). The inclusion of carbon in alpha iron is called ferrite . At 910 °C, pure iron transforms into a face-centred cubic (FCC) structure, called gamma iron or γ-iron. The inclusion of carbon in gamma iron is called austenite. The more open FCC structure of austenite can dissolve considerably more carbon, as much as 2.1%, (38 times that of ferrite) carbon at 1,148 °C (2,098 °F), which reflects

1952-453: A steel's final rolling, it is heat treated for strength; however, this is relatively rare. Steel was known in antiquity and was produced in bloomeries and crucibles . The earliest known production of steel is seen in pieces of ironware excavated from an archaeological site in Anatolia ( Kaman-Kalehöyük ) which are nearly 4,000 years old, dating from 1800 BC. Wootz steel

2074-477: A subsequent step. Other materials are often added to the iron/carbon mixture to produce steel with the desired properties. Nickel and manganese in steel add to its tensile strength and make the austenite form of the iron-carbon solution more stable, chromium increases hardness and melting temperature, and vanadium also increases hardness while making it less prone to metal fatigue . To inhibit corrosion, at least 11% chromium can be added to steel so that

2196-415: A tragic ending in 1937. After Fillunger’s suicide, his theoretical results were forgotten for decades, whereas the methods proposed by Terzaghi found widespread diffusion among scientists and professionals. In the following decades Biot fully developed the three-dimensional soil consolidation theory, extending the one-dimensional model previously proposed by Terzaghi to more general hypotheses and introducing

2318-672: Is continuously cast into long slabs, cut and shaped into bars and extrusions and heat treated to produce a final product. Today, approximately 96% of steel is continuously cast, while only 4% is produced as ingots. The ingots are then heated in a soaking pit and hot rolled into slabs, billets , or blooms . Slabs are hot or cold rolled into sheet metal or plates. Billets are hot or cold rolled into bars, rods, and wire. Blooms are hot or cold rolled into structural steel , such as I-beams and rails . In modern steel mills these processes often occur in one assembly line , with ore coming in and finished steel products coming out. Sometimes after

2440-441: Is overconsolidated up to a depth of approximately 70 feet (20 m; 10 sm). The substructure originally consisted of two masonry abutments and twenty-three masonry piers, as well as one pile foundation with a fender pier for the draw span. The superstructure was originally twenty-three cantilevered fixed spans and suspended spans, of plate girders with one swing span . The Boston abutment rests on vertical piles, while

2562-446: Is "any process which involves a decrease in water content of saturated soil without replacement of water by air". More generally, consolidation refers to the process by which soils change volume in response to a change in pressure , encompassing both compaction and swelling. Consolidation is the process in which reduction in volume takes place by the gradual expulsion or absorption of water under long-term static loads. When stress

SECTION 20

#1732772046470

2684-409: Is 95% Where T 95 =1.129 T 50 =0.197 The theoretical formulation above assumes that time-dependent volume change of a soil unit only depends on changes in effective stress due to the gradual restoration of steady-state pore water pressure. This is the case for most types of sand and clay with low amounts of organic material. However, in soils with a high amount of organic material such as peat ,

2806-636: Is also very reusable: it is one of the world's most-recycled materials, with a recycling rate of over 60% globally . The noun steel originates from the Proto-Germanic adjective * * stahliją or * * stakhlijan 'made of steel', which is related to * * stahlaz or * * stahliją 'standing firm'. The carbon content of steel is between 0.02% and 2.14% by weight for plain carbon steel ( iron - carbon alloys ). Too little carbon content leaves (pure) iron quite soft, ductile, and weak. Carbon contents higher than those of steel make

2928-416: Is always the main element in steel, but many other elements may be present or added. Stainless steels , which are resistant to corrosion and oxidation , typically need an additional 11% chromium . Iron is the base metal of steel. Depending on the temperature, it can take two crystalline forms (allotropic forms): body-centred cubic and face-centred cubic . The interaction of the allotropes of iron with

3050-432: Is an alloy of iron and carbon with improved strength and fracture resistance compared to other forms of iron. Because of its high tensile strength and low cost, steel is one of the most commonly manufactured materials in the world. Steel is used in buildings, as concrete reinforcing rods, in bridges, infrastructure, tools, ships, trains, cars, bicycles, machines, electrical appliances, furniture, and weapons. Iron

3172-412: Is applied to a soil, it causes the soil particles to pack together more tightly. When this occurs in a soil that is saturated with water, water will be squeezed out of the soil. The magnitude of consolidation can be predicted by many different methods. In the classical method developed by Terzaghi, soils are tested with an oedometer test to determine their compressibility. In most theoretical formulations,

3294-403: Is common for quench cracks to form when steel is water quenched, although they may not always be visible. There are many types of heat treating processes available to steel. The most common are annealing , quenching , and tempering . Annealing is the process of heating the steel to a sufficiently high temperature to relieve local internal stresses. It does not create a general softening of

3416-422: Is considered to be "overconsolidated". This is the case for soils that have previously had glaciers on them or that have been affected by land subsidence . The highest stress that it has been subjected to is termed the " preconsolidation stress ". The "over-consolidation ratio" (OCR) is defined as the highest stress experienced divided by the current stress. A soil that is currently experiencing its highest stress

3538-403: Is desirable. To become steel, it must be reprocessed to reduce the carbon to the correct amount, at which point other elements can be added. In the past, steel facilities would cast the raw steel product into ingots which would be stored until use in further refinement processes that resulted in the finished product. In modern facilities, the initial product is close to the final composition and

3660-571: Is especially true in saturated clays because their hydraulic conductivity is extremely low, and this causes the water to take an exceptionally long time to drain out of the soil. While drainage is occurring, the pore water pressure is greater than normal because it is carrying part of the applied stress (as opposed to the soil particles). T v = c v ∗ t ( H d r ) 2   {\displaystyle T_{v}={\frac {c_{v}*t}{(H_{dr})^{2}}}\ } Where T v

3782-405: Is extracted from iron ore by removing the oxygen through its combination with a preferred chemical partner such as carbon which is then lost to the atmosphere as carbon dioxide. This process, known as smelting , was first applied to metals with lower melting points, such as tin , which melts at about 250 °C (482 °F), and copper , which melts at about 1,100 °C (2,010 °F), and

Harvard Bridge - Misplaced Pages Continue

3904-408: Is heat treated to contain both a ferritic and martensitic microstructure to produce a formable, high strength steel. Transformation Induced Plasticity (TRIP) steel involves special alloying and heat treatments to stabilize amounts of austenite at room temperature in normally austenite-free low-alloy ferritic steels. By applying strain, the austenite undergoes a phase transition to martensite without

4026-462: Is known as "intrinsic consolidation". The process of consolidation is often explained with an idealized system composed of a spring , a container with a hole in its cover, and water. In this system, the spring represents the compressibility or the structure of the soil itself, and the water which fills the container represents the pore water in the soil. The time for consolidation to occur can be predicted. Sometimes consolidation can take years. This

4148-528: Is known locally for being marked off in the idiosyncratic unit of length called the smoot . In 1874 the Massachusetts Legislature authorized construction of a bridge between Boston and Cambridge, and in 1882 follow-up legislation set out its location. The bridge was to have a draw with an opening of at least 38 feet (12 m; 6.8 sm). Boston interests opposed the bridge, mainly because it did not provide for an overhead crossing of

4270-515: Is now connected with the choicest residential portions of Boston. The residents of the Back Bay, South End, Roxbury, and other southern sections of Boston are now connected directly, by way of West Chester park and the bridge, with Cambridge, Belmont, Arlington, and adjacent towns; and this thoroughfare in Boston, it is believed, will ultimately be the central one of the city. The bridge is named for

4392-691: Is often considered an indicator of economic progress, because of the critical role played by steel in infrastructural and overall economic development . In 1980, there were more than 500,000 U.S. steelworkers. By 2000, the number of steelworkers had fallen to 224,000. The economic boom in China and India caused a massive increase in the demand for steel. Between 2000 and 2005, world steel demand increased by 6%. Since 2000, several Indian and Chinese steel firms have expanded to meet demand, such as Tata Steel (which bought Corus Group in 2007), Baosteel Group and Shagang Group . As of 2017 , though, ArcelorMittal

4514-551: Is one of the world's most-recycled materials, with a recycling rate of over 60% globally; in the United States alone, over 82,000,000 metric tons (81,000,000 long tons; 90,000,000 short tons) were recycled in the year 2008, for an overall recycling rate of 83%. As more steel is produced than is scrapped, the amount of recycled raw materials is about 40% of the total of steel produced - in 2016, 1,628,000,000 tonnes (1.602 × 10 long tons; 1.795 × 10 short tons) of crude steel

4636-423: Is removed from a consolidated soil, the soil will rebound, regaining some of the volume it had lost in the consolidation process. If the stress is reapplied, the soil will consolidate again along a recompression curve, defined by the recompression index. The gradient of the swelling and recompression lines on a plot of void ratio against the logarithm of effective stress often idealised to take the same value, known as

4758-401: Is said to be "normally consolidated" and has an OCR of one. A soil could be considered "underconsolidated" or "unconsolidated" immediately after a new load is applied but before the excess pore water pressure has dissipated. Occasionally, soil strata form by natural deposition in rivers and seas may exist in an exceptionally low density that is impossible to achieve in an oedometer; this process

4880-476: Is the preconsolidation stress of the soil. This method assumes consolidation occurs in only one-dimension. Laboratory data is used to construct a plot of strain or void ratio versus effective stress where the effective stress axis is on a logarithmic scale . The plot's slope is the compression index or recompression index. The equation for consolidation settlement of a normally consolidated soil can then be determined to be: The soil which had its load removed

5002-666: Is the time factor. H dr is the average longest drain path during consolidation. t is the time at measurement C v is defined as the coefficient of consolidation found using the log method with C v = T 50 H d r 2 t 50 {\displaystyle C_{v}={\frac {T_{50}H_{dr}^{2}}{t_{50}}}} or the root method with C v = T 95 H d r 2 t 95 {\displaystyle C_{v}={\frac {T_{95}H_{dr}^{2}}{t_{95}}}} t 50 time to 50% deformation (consolidation) and t 95

Harvard Bridge - Misplaced Pages Continue

5124-547: Is the world's largest steel producer . In 2005, the British Geological Survey stated China was the top steel producer with about one-third of the world share; Japan , Russia , and the United States were second, third, and fourth, respectively, according to the survey. The large production capacity of steel results also in a significant amount of carbon dioxide emissions inherent related to

5246-463: The Department of Conservation and Recreation ) in 1971–1972 due to complaints by bridge users of excessive vibration. The bridge was found to be understrength for its load. Before the final study was complete, the recommendation was to place a load limit of 8 short tons (7.3  t ) per axle and a total of 15 short tons (14 t) per vehicle, or to restrict trucks to the interior lanes, where

5368-655: The Golconda area in Andhra Pradesh and Karnataka , regions of India , as well as in Samanalawewa and Dehigaha Alakanda, regions of Sri Lanka . This came to be known as wootz steel , produced in South India by about the sixth century BC and exported globally. The steel technology existed prior to 326 BC in the region as they are mentioned in literature of Sangam Tamil , Arabic, and Latin as

5490-586: The Grand Junction Branch of the Boston and Albany Railroad . Further legislation in 1885 changed the draw to a clear opening of at least 36 feet (11 m; 6.4 sm) and no more, until the other bridges below the proposed location were required to have a larger opening. There was still no substantive progress until 1887, when Cambridge petitioned the Legislature to compel Boston to proceed;

5612-552: The Reverend John Harvard , for whom Harvard University is also named, rather than for the university itself. Other names suggested included Blaxton , Chester , Shawmut , and Longfellow . Originally projected as a wooden pile structure with stone pavement for the first 200 feet (61 m; 36 sm) (because the Charles River Embankment extension was expected to take that space) the design

5734-599: The cementation process was described in a treatise published in Prague in 1574 and was in use in Nuremberg from 1601. A similar process for case hardening armour and files was described in a book published in Naples in 1589. The process was introduced to England in about 1614 and used to produce such steel by Sir Basil Brooke at Coalbrookdale during the 1610s. The raw material for this process were bars of iron. During

5856-419: The hardness , quenching behaviour , need for annealing , tempering behaviour , yield strength , and tensile strength of the resulting steel. The increase in steel's strength compared to pure iron is possible only by reducing iron's ductility. Steel was produced in bloomery furnaces for thousands of years, but its large-scale, industrial use began only after more efficient production methods were devised in

5978-420: The mixture theory . Terzaghi had an engineering approach to the problem of soil consolidation and provided simplified models that are still widely used in engineering practice today, whereas, on the other hand, Fillunger had a rigorous approach to the above problems and provided rigorous mathematical models that paid particular attention to the methods of local averaging of the involved variables. Fillunger’s model

6100-416: The "swelling index" (given the symbol κ {\displaystyle \kappa } when calculated in natural logarithm and C S {\displaystyle C_{S}} when calculated in base-10 logarithm). C c can be replaced by C r (the recompression index) for use in overconsolidated soils where the final effective stress is less than the preconsolidation stress. When

6222-445: The 17th century, it was realized that the best steel came from oregrounds iron of a region north of Stockholm , Sweden. This was still the usual raw material source in the 19th century, almost as long as the process was used. Crucible steel is steel that has been melted in a crucible rather than having been forged , with the result that it is more homogeneous. Most previous furnaces could not reach high enough temperatures to melt

SECTION 50

#1732772046470

6344-475: The 17th century, the first step in European steel production has been the smelting of iron ore into pig iron in a blast furnace . Originally employing charcoal, modern methods use coke , which has proven more economical. In these processes, pig iron made from raw iron ore was refined (fined) in a finery forge to produce bar iron , which was then used in steel-making. The production of steel by

6466-626: The 17th century, with the introduction of the blast furnace and production of crucible steel . This was followed by the Bessemer process in England in the mid-19th century, and then by the open-hearth furnace . With the invention of the Bessemer process, a new era of mass-produced steel began. Mild steel replaced wrought iron . The German states were the major steel producers in Europe in

6588-481: The 19th century. American steel production was centred in Pittsburgh , Bethlehem, Pennsylvania , and Cleveland until the late 20th century. Currently, world steel production is centered in China, which produced 54% of the world's steel in 2023. Further refinements in the process, such as basic oxygen steelmaking (BOS), largely replaced earlier methods by further lowering the cost of production and increasing

6710-608: The Arabs from Persia, who took it from India. It was originally created from several different materials including various trace elements , apparently ultimately from the writings of Zosimos of Panopolis . In 327 BC, Alexander the Great was rewarded by the defeated King Porus , not with gold or silver but with 30 pounds of steel. A recent study has speculated that carbon nanotubes were included in its structure, which might explain some of its legendary qualities, though, given

6832-615: The Cambridge end is directly on gravel. Originally, the bridge was built across the Charles River connecting West Chester Park, in Boston, with Front Street, in Cambridge. This is now called Massachusetts Avenue on both sides of the river. As originally built, the total length between centers of bearings on abutments was 2,164 feet 9 inches (659.82 m; 387.72 sm) with a draw 48 feet 4 inches (14.73 m; 8.66 sm) wide between centers. The width of

6954-466: The Cambridge end of the bridge led to the construction of an underpass in 1931. The bridge was formerly referred to as the "Xylophone Bridge" because of the sound its wooden decking made when traffic traveled over it. This decking was replaced in 1949 with 3-inch (76 mm; 0.045 sm) concrete-filled "I-beam lok" grating topped with a 2.25-inch (57 mm; 0.0336 sm) thick bituminous wearing surface. At this time, all bearings were replaced, and

7076-470: The Linz-Donawitz process of basic oxygen steelmaking (BOS), developed in 1952, and other oxygen steel making methods. Basic oxygen steelmaking is superior to previous steelmaking methods because the oxygen pumped into the furnace limited impurities, primarily nitrogen, that previously had entered from the air used, and because, with respect to the open hearth process, the same quantity of steel from

7198-411: The action of external loads (surcharge loads) but also under its own weight or weight of soils that exist above the clay. Clays also undergo settlement when dewatered (groundwater pumping) because the effective stress on the clay increases. Coarse-grained soils do not undergo consolidation settlement due to relatively high hydraulic conductivity compared to clays. Instead, Coarse-grained soils undergo

7320-454: The addition of heat. Twinning Induced Plasticity (TWIP) steel uses a specific type of strain to increase the effectiveness of work hardening on the alloy. Consolidation (soil) In the narrow sense, "consolidation" refers strictly to this delayed volumetric response to pressure change due to gradual movement of water. Some publications also use "consolidation" in the broad sense, to refer to any process by which soil changes volume due to

7442-401: The alloying elements, primarily carbon, gives steel and cast iron their range of unique properties. In pure iron, the crystal structure has relatively little resistance to the iron atoms slipping past one another, and so pure iron is quite ductile , or soft and easily formed. In steel, small amounts of carbon, other elements, and inclusions within the iron act as hardening agents that prevent

SECTION 60

#1732772046470

7564-436: The austenite grain boundaries until the percentage of carbon in the grains has decreased to the eutectoid composition (0.8% carbon), at which point the pearlite structure forms. For steels that have less than 0.8% carbon (hypoeutectoid), ferrite will first form within the grains until the remaining composition rises to 0.8% of carbon, at which point the pearlite structure will form. No large inclusions of cementite will form at

7686-471: The austenite is for it to precipitate out of solution as cementite , leaving behind a surrounding phase of BCC iron called ferrite with a small percentage of carbon in solution. The two, cementite and ferrite, precipitate simultaneously producing a layered structure called pearlite , named for its resemblance to mother of pearl . In a hypereutectoid composition (greater than 0.8% carbon), the carbon will first precipitate out as large inclusions of cementite at

7808-494: The boundaries in hypoeutectoid steel. The above assumes that the cooling process is very slow, allowing enough time for the carbon to migrate. As the rate of cooling is increased the carbon will have less time to migrate to form carbide at the grain boundaries but will have increasingly large amounts of pearlite of a finer and finer structure within the grains; hence the carbide is more widely dispersed and acts to prevent slip of defects within those grains, resulting in hardening of

7930-417: The bridge was 69 feet 4 inches (21.13 m; 12.42 sm) except near and on the draw. The bridge as built was composed of fixed and suspended spans roughly 75 feet (23 m; 13.4 sm) long and piers 90 feet (27 m; 16 sm) apart, center to center. The span lengths alternated between 75 and 105 feet (23 and 32 m; 13.4 and 18.8 sm). The longer spans were cantilevered, while

8052-401: The bridge was stronger. A 25-short-ton (23 t) limit was imposed. Suggestions made included strengthening the existing structure by adding either struts or plates to make the existing four beams along the length of the bridge into a stiffening truss, or to replace the superstructure with a new one, made of either steel or concrete, which would be up to current standards. The recommendation

8174-611: The bridge's eastern sidewalk by using that year's shortest pledge , Oliver Smoot ‍—‌nominally, 5 feet 7 inches (1.70 m) tall‍—‌as a measuring stick. Years after this stunt, Smoot became president of the American National Standards Institute (ANSI), and later president of the International Organization for Standardization (ISO). Markers painted at 10-smoot (55.83 ft; 17.02 m) intervals give

8296-469: The bridge's ends) corresponds to about 2030 feet or 620 m, somewhat less than the bridge's published length of 2,170 feet; 390 smoots (660 m). A possible cause is that in 1958, there were ramps to Storrow Drive on both sides of the bridge, which interrupted the sidewalk earlier than it extends today. A bridge of 2,164.8 feet (659.82 m) corresponds to 387.7 smoots ± one ear. Informational notes Citations Bibliography Steel Steel

8418-444: The bridge's length 364.4 smoots long, "plus one ear". Originally this read "plus or minus one ear"‍—‌representing measurement uncertainty‍—‌but over the years the words "or minus" disappeared. The marks are repainted periodically by members of the fraternity‍—‌originally surreptitiously and later openly. During the major reconstruction in the 1980s, the new sidewalks were divided into smoot -length slabs rather than

8540-484: The cities of Boston and Cambridge, the bridge was built jointly by the two cities between 1887 and 1891. It was named for Harvard University founder John Harvard . Originally equipped with a central swing span , it was revised several times over the years until its superstructure was completely replaced in the late 1980s due to unacceptable vibration and the collapse of a similar bridge in Connecticut. The bridge

8662-455: The combination, bronze, which has a melting point lower than 1,083 °C (1,981 °F). In comparison, cast iron melts at about 1,375 °C (2,507 °F). Small quantities of iron were smelted in ancient times, in the solid-state, by heating the ore in a charcoal fire and then welding the clumps together with a hammer and in the process squeezing out the impurities. With care, the carbon content could be controlled by moving it around in

8784-605: The corridor. These changes were implemented just before 2023, and have been in place since. To this date, the Harvard Bridge remains one of the most popular cycling routes in New England, with an average of over 1,000 bicyclists in each direction per day. The Harvard Bridge is marked off in an idiosyncratic unit of measure, the smoot . In 1958, members of the Lambda Chi Alpha fraternity at MIT measured

8906-472: The creep process. The effects of consolidation are most conspicuous where a building sits over a layer of soil with low stiffness and low permeability, such as marine clay , leading to large settlement over many years. Types of construction project where consolidation often poses technical risk include land reclamation , the construction of embankments , and tunnel and basement excavation in clay. Geotechnical engineers use oedometers to quantify

9028-545: The date as April 30, 1908.) The bridge was declared unsafe in 1909, requiring all of the iron and steel to be replaced. The draw was elevated slightly and the trolley rails were replaced as well. When the Metropolitan District Commission (MDC) took control of the bridge in 1924, they rebuilt much of the bridge superstructure. They replaced the wooden stringers with steel "I" beams, topped wooden deck elements with concrete and brick, and replaced

9150-461: The designation "secondary" distinguishes it from "primary consolidation", which refers to volume change due to dissipation of excess pore water pressure. Creep typically takes place over a longer time-scale than (primary) consolidation, such that even after the restoration of hydrostatic pressure some compression of soil takes place at slow rate. Analytically, the rate of creep is assumed to decay exponentially with time since application of load, giving

9272-406: The discovery of two failed hangers on span 14. A few days later, all trucks and buses were banned from the bridge. In 1986, a report was published containing the plan to replace the superstructure on the existing supports. Alternatives considered were very similar to the 1972 report , and were similarly decided. Structural modifications included an upgrade from four longitudinal girders to six of

9394-452: The economies of melting and casting, can be heat treated after casting to make malleable iron or ductile iron objects. Steel is distinguishable from wrought iron (now largely obsolete), which may contain a small amount of carbon but large amounts of slag . Iron is commonly found in the Earth's crust in the form of an ore , usually an iron oxide, such as magnetite or hematite . Iron

9516-494: The effects of consolidation. In an oedometer test, a series of known pressures are applied to a thin disc of soil sample, and the change of sample thickness with time is recorded. This allows the consolidation characteristics of the soil to be quantified in terms of the coefficient of consolidation ( C v {\displaystyle C_{v}} ) and hydraulic conductivity ( K {\displaystyle K} ). Clays undergo consolidation settlement not only by

9638-435: The existing structure would leave old wrought iron of uncertain quality and condition standing, and would not bring the design up to (then) current standards. Detailed engineering calculations were included. The price was estimated at US$ 2.5 million to US$ 3 million (US$ 18,000,000 to US$ 22,000,000 with inflation). The action taken based on this study was to establish load restrictions on the bridge, 15 short tons (14 t) in

9760-898: The final effective stress is greater than the preconsolidation stress, the two equations must be used in combination to model both the recompression portion and the virgin compression portion of the consolidation processes, as follows, δ c = C r 1 + e 0 H log ⁡ ( σ z c ′ σ z 0 ′ ) + C c 1 + e 0 H log ⁡ ( σ z f ′ σ z c ′ )   {\displaystyle \delta _{c}={\frac {C_{r}}{1+e_{0}}}H\log \left({\frac {\sigma _{zc}'}{\sigma _{z0}'}}\right)+{\frac {C_{c}}{1+e_{0}}}H\log \left({\frac {\sigma _{zf}'}{\sigma _{zc}'}}\right)\ } where σ zc

9882-648: The finest steel in the world exported to the Roman, Egyptian, Chinese and Arab worlds at that time – what they called Seric Iron . A 200 BC Tamil trade guild in Tissamaharama , in the South East of Sri Lanka, brought with them some of the oldest iron and steel artifacts and production processes to the island from the classical period . The Chinese and locals in Anuradhapura , Sri Lanka had also adopted

10004-579: The fire. Unlike copper and tin, liquid or solid iron dissolves carbon quite readily. All of these temperatures could be reached with ancient methods used since the Bronze Age . Since the oxidation rate of iron increases rapidly beyond 800 °C (1,470 °F), it is important that smelting take place in a low-oxygen environment. Smelting, using carbon to reduce iron oxides, results in an alloy ( pig iron ) that retains too much carbon to be called steel. The excess carbon and other impurities are removed in

10126-475: The following equation, which is used to estimate the volume change of a soil layer: δ c = C c 1 + e 0 H log ⁡ ( σ z f ′ σ z 0 ′ )   {\displaystyle \delta _{c}={\frac {C_{c}}{1+e_{0}}}H\log \left({\frac {\sigma _{zf}'}{\sigma _{z0}'}}\right)\ } where When stress

10248-513: The form of charcoal) in a crucible, was produced in Merv by the 9th to 10th century AD. In the 11th century, there is evidence of the production of steel in Song China using two techniques: a "berganesque" method that produced inferior, inhomogeneous steel, and a precursor to the modern Bessemer process that used partial decarburization via repeated forging under a cold blast . Since

10370-399: The formula: S s = H 0 1 + e 0 C a log ⁡ ( t t 95 )   {\displaystyle S_{s}={\frac {H_{0}}{1+e_{0}}}C_{a}\log \left({\frac {t}{t_{95}}}\right)\ } Where H 0 is the height of the consolidating medium e 0 is the initial void ratio C

10492-599: The hardenability of thick sections. High strength low alloy steel has small additions (usually < 2% by weight) of other elements, typically 1.5% manganese, to provide additional strength for a modest price increase. Recent corporate average fuel economy (CAFE) regulations have given rise to a new variety of steel known as Advanced High Strength Steel (AHSS). This material is both strong and ductile so that vehicle structures can maintain their current safety levels while using less material. There are several commercially available grades of AHSS, such as dual-phase steel , which

10614-463: The immediate settlement. The first modern theoretical models for soil consolidation were proposed in the 1920s by Terzaghi and Fillunger , according to two substantially different approaches. The former was based on diffusion equations in eulerian notation , whereas the latter considered the local Newton’s law for both liquid and solid phases, in which main variables, such as partial pressure, porosity, local velocity etc., were involved by means of

10736-439: The main production route. At the end of 2008, the steel industry faced a sharp downturn that led to many cut-backs. In 2021, it was estimated that around 7% of the global greenhouse gas emissions resulted from the steel industry. Reduction of these emissions are expected to come from a shift in the main production route using cokes, more recycling of steel and the application of carbon capture and storage technology. Steel

10858-441: The mayors. The mayors of Boston and Cambridge, Hugh O'Brien and William E. Russell , appointed Leander Greeley of Cambridge as the third commissioner, though this appointment changed over time. The commission's 1892 report claimed: The effect that the bridge will have upon both cities is obvious. The low land and marshes on the Cambridge side, formerly almost valueless, have been filled in and have become valuable; and Cambridge

10980-450: The most part, however, p-block elements such as sulphur, nitrogen , phosphorus , and lead are considered contaminants that make steel more brittle and are therefore removed from steel during the melting processing. The density of steel varies based on the alloying constituents but usually ranges between 7,750 and 8,050 kg/m (484 and 503 lb/cu ft), or 7.75 and 8.05 g/cm (4.48 and 4.65 oz/cu in). Even in

11102-446: The movement of dislocations . The carbon in typical steel alloys may contribute up to 2.14% of its weight. Varying the amount of carbon and many other alloying elements, as well as controlling their chemical and physical makeup in the final steel (either as solute elements, or as precipitated phases), impedes the movement of the dislocations that make pure iron ductile, and thus controls and enhances its qualities. These qualities include

11224-608: The order kaolinite <illite<smectite. The compression index Cc, which is defined as the change in void ratio per 10-fold increase in consolidation pressure, is in the range of 0.19 to 0.28 for kaolinite, 0.50 to 1.10 for illite, and 1.0 to 2.6 for montmorillonite, for different ionic forms. The more compressible the clay, the more pronounced the influences of cation type and electrolyte concentration on compressibility. Coefficient of volume compressibility m v = Δ V / V Δ σ ′ =

11346-485: The outer lanes, 25 short tons (23 t) on the inner lanes. This was expanded in 1979 to a flat limit of 15 short tons (14 t) on the whole bridge. After the failure of the Mianus River Bridge at Greenwich, Connecticut in 1983, the Harvard Bridge was shut down and inspected because it contained similar elements, specifically the suspended spans. Traffic was restricted to the inner two lanes due to

11468-414: The phenomenon of creep also occurs, whereby the soil changes volume gradually at constant effective stress. Soil creep is typically caused by viscous behavior of the clay-water system and compression of organic matter. This process of creep is sometimes known as "secondary consolidation" or "secondary compression" because it also involves gradual change of soil volume in response to an application of load;

11590-449: The product but only locally relieves strains and stresses locked up within the material. Annealing goes through three phases: recovery , recrystallization , and grain growth . The temperature required to anneal a particular steel depends on the type of annealing to be achieved and the alloying constituents. Quenching involves heating the steel to create the austenite phase then quenching it in water or oil . This rapid cooling results in

11712-759: The production methods of creating wootz steel from the Chera Dynasty Tamils of South India by the 5th century AD. In Sri Lanka, this early steel-making method employed a unique wind furnace, driven by the monsoon winds, capable of producing high-carbon steel. Since the technology was acquired from the Tamilians from South India, the origin of steel technology in India can be conservatively estimated at 400–500 BC. The manufacture of wootz steel and Damascus steel , famous for its durability and ability to hold an edge, may have been taken by

11834-426: The quality of the final product. Today more than 1.6 billion tons of steel is produced annually. Modern steel is generally identified by various grades defined by assorted standards organizations . The modern steel industry is one of the largest manufacturing industries in the world, but also one of the most energy and greenhouse gas emission intense industries, contributing 8% of global emissions. However, steel

11956-415: The resulting act required each city pay half the cost, and allowed Boston to raise up to $ 250,000 (US$ 8,480,000 with inflation) for this purpose, in excess of its debt limit . This implied an estimated cost of US$ 500,000 (US$ 17,000,000 with inflation) for the bridge. The Legislature provided for a bridge commission, to consist of the mayors of Boston and Cambridge plus a third commissioner to be appointed by

12078-457: The same shape and replacement of a stairway with a handicapped pedestrian ramp on the Boston end of the bridge. Ramp "B", from southbound (Boston bound) bridge lanes to eastbound Storrow Drive , caused traffic to merge onto Storrow Drive from the left (high speed) lanes using a short acceleration lane, causing safety issues. The MDC requested elimination of this ramp. Compared to overall bridge traffic of 30,000 vehicles per day, traffic on ramp B

12200-494: The set of basic equations of poroelasticity . Today, the Terzaghis’ one dimensional model is still the most utilized by engineers for its conceptual simplicity and because it is based on experimental data, such as oedometer tests , which are relatively simple, reliable and inexpensive and for which theoretical solutions in closed form are well known. According to the "father of soil mechanics ", Karl von Terzaghi , consolidation

12322-435: The shorter spans were suspended between the cantilevers. The original roadway contained two lanes for horse-drawn vehicles and two street car tracks, for a total width of 51.0 feet (15.5 m; 9.13 sm). There were also two 9-foot-2-inch (2.79 m; 1.64 sm) sidewalks. The original roadway and sidewalk stringers were of wood, with an approximately 1.25-inch (32 mm; 0.0187 sm) thick covering of asphalt on

12444-456: The sidewalk and a 2-inch (51 mm; 0.030 sm) spruce wearing surface on the roadway. The exception was at the swing span, which was 48 feet (15 m; 8.6 sm) wide. This span was approximately 149 feet (45 m; 26.7 sm) long, and sat on a wooden pier. It was a double-cantilevered, electrically-driven structure also carrying a bridge caretaker's house. The bridge opened on September 1, 1891. The original cost of construction

12566-464: The situation at the bridge is exacerbated by a fault which roughly follows the path of the Charles River itself. From a depth of approximately 200 to 300 feet (60 to 90 m; 40 to 50 sm) below existing ground, is a very dense till composed of gravel and boulders with a silt-clay matrix. Above that to approximately 30 feet (9 m; 5 sm) below the surface is Boston blue clay (BBC). Over this are thin layers of sand, gravel, and fill. The BBC

12688-417: The standard six feet, and the smoot markings were painted on the new deck. Officials' original determination to omit the smoot markings from the reconstructed bridge, and to scrupulously prevent the fraternity from repainting them, evaporated when it was realized that police routinely used the smoot marks as reference points in accident reports. The nominal length of 364.4 smoots (from two designated points at

12810-401: The steel. At the very high cooling rates produced by quenching, the carbon has no time to migrate but is locked within the face-centred austenite and forms martensite . Martensite is a highly strained and stressed, supersaturated form of carbon and iron and is exceedingly hard but brittle. Depending on the carbon content, the martensitic phase takes different forms. Below 0.2% carbon, it takes on

12932-561: The steel. The early modern crucible steel industry resulted from the invention of Benjamin Huntsman in the 1740s. Blister steel (made as above) was melted in a crucible or in a furnace, and cast (usually) into ingots. The modern era in steelmaking began with the introduction of Henry Bessemer 's process in 1855, the raw material for which was pig iron. His method let him produce steel in large quantities cheaply, thus mild steel came to be used for most purposes for which wrought iron

13054-472: The street car rails. Structural steel hangers replaced wrought iron. The swing span was converted into two 75-foot (23 m; 13.4 sm) fixed spans the same width as the rest of the bridge. The wooden pier was heavily modified with concrete and stone to make it resemble the other piers, increasing the number of stone piers from 23 to 24. Heavy traffic at the Mass Ave and Memorial Drive intersection on

13176-561: The technology of that time, such qualities were produced by chance rather than by design. Natural wind was used where the soil containing iron was heated by the use of wood. The ancient Sinhalese managed to extract a ton of steel for every 2 tons of soil, a remarkable feat at the time. One such furnace was found in Samanalawewa and archaeologists were able to produce steel as the ancients did. Crucible steel , formed by slowly heating and cooling pure iron and carbon (typically in

13298-433: The trolley car tracks were removed, as were granite blocks. The trolley car poles were reused for street lights. Ramps between the bridge and the under-construction Storrow Drive were added. The 1924 sidewalk slabs were replaced by precast, prestressed slabs in 1962. The fifteen expansion dams were replaced or repaired in 1969. An engineering study was performed by the Metropolitan District Commission (later merged into

13420-525: The upper carbon content of steel, beyond which is cast iron. When carbon moves out of solution with iron, it forms a very hard, but brittle material called cementite (Fe 3 C). When steels with exactly 0.8% carbon (known as a eutectoid steel), are cooled, the austenitic phase (FCC) of the mixture attempts to revert to the ferrite phase (BCC). The carbon no longer fits within the FCC austenite structure, resulting in an excess of carbon. One way for carbon to leave

13542-478: Was $ 511,000, $ 17,330,000 in current dollars. In 1898, 3-foot-wide (0.91 m; 0.54 sm) bicycle lanes were installed next to each curb. In 2011 (113 years later), the City of Boston finally connected these lanes to its own bike lanes. A marker near the southeast end of the bridge memorializes one of Harry Houdini 's "well known escapes", during which he jumped from the bridge on May 1, 1908. (Other sources give

13664-415: Was changed to be entirely iron spans on stone piers. The general plans were approved on July 14, 1887. The engineers were William Jackson (Boston City Engineer), John E. Cheney (assistant Boston City Engineer), Samuel E. Tinkham (assistant engineer), and Nathan S. Brock (assistant engineer at bridge). The subsurface conditions at the bridge location are extreme. Much of Boston is underlain with clay, but

13786-718: Was developed in Southern India and Sri Lanka in the 1st millennium BCE. Metal production sites in Sri Lanka employed wind furnaces driven by the monsoon winds, capable of producing high-carbon steel. Large-scale wootz steel production in India using crucibles occurred by the sixth century BC, the pioneering precursor to modern steel production and metallurgy. High-carbon steel was produced in Britain at Broxmouth Hillfort from 490–375 BC, and ultrahigh-carbon steel

13908-494: Was estimated to be US$ 20M (US$ 56,000,000 with inflation). Phase 1 finished in 1987, and Phase 2 in 1990. In the fall of 2014, the Charles River Conservancy announced that an anonymous donor would fund an upgrade of the street lights for both the roadway and both sidewalks on the bridge. The new roadway and aesthetic lighting was installed in 2015, highlighting the smoot marks along the sidewalk. The design

14030-509: Was formerly used. The Gilchrist-Thomas process (or basic Bessemer process ) was an improvement to the Bessemer process, made by lining the converter with a basic material to remove phosphorus. Another 19th-century steelmaking process was the Siemens-Martin process , which complemented the Bessemer process. It consisted of co-melting bar iron (or steel scrap) with pig iron. These methods of steel production were rendered obsolete by

14152-431: Was found to be low, approximately 1,500 vehicles per day with a peak of 120 vehicles per hour. The historic value of the bridge was considered significant, so the plan was to make the replacement superstructure appear similar, with similar railing and lighting. In order to document the pre-existing structure, a Historic American Engineering Record (HAER) would be prepared. Pier 12 was exhibiting inappropriate movement and

14274-438: Was produced globally, with 630,000,000 tonnes (620,000,000 long tons; 690,000,000 short tons) recycled. Modern steels are made with varying combinations of alloy metals to fulfil many purposes. Carbon steel , composed simply of iron and carbon, accounts for 90% of steel production. Low alloy steel is alloyed with other elements, usually molybdenum , manganese, chromium, or nickel, in amounts of up to 10% by weight to improve

14396-757: Was produced in the Netherlands from the 2nd-4th centuries AD. The Roman author Horace identifies steel weapons such as the falcata in the Iberian Peninsula , while Noric steel was used by the Roman military . The Chinese of the Warring States period (403–221 BC) had quench-hardened steel, while Chinese of the Han dynasty (202 BC—AD 220) created steel by melting together wrought iron with cast iron, thus producing

14518-420: Was scheduled for reinforcement. The work would be done in two phases. Phase 1 would reinforce the downstream side of the bridge to allow MBTA bus traffic, and was expected to take 5 months. Most of this effort would be spent on the underside of the bridge and would not affect existing traffic. Phase 2 would replace the entire superstructure and was expected to take three construction seasons to implement. Cost

14640-485: Was selected after a competition won by Miguel Rosales of Rosales + Partners. The light posts will be located 30 smoots (167.5 ft; 51.05 m) apart. "It will provide safe lighting for pedestrians and drivers, and the elements of design on the bridge will be pulled out and emphasized. It will become a really beautiful bridge," said Renata von Tscharner, founder and president of the Charles River Conservancy. In November 2021, to improve bicycle safety, MassDOT initiated

14762-459: Was to replace the superstructure with one weighing approximately the same in order to reuse the piers, which were in good condition. The reasoning was that the cost of a new structure could be predicted much more easily than the cost of repairing and reinforcing the existing bridge. The resulting new bridge would be of known materials and quality, such as ductile structural steel rather than brittle wrought iron, and rated at AASHO HS-20. Repairing

14884-450: Was very abstract and involved variables that were difficult to detect experimentally, and, therefore, it was not applicable to the study of real cases by engineers and/or designers. Nevertheless, this provided the basis for advanced theoretical studies of particularly complex problems. Due to the different approach to the problem of consolidation by the two scientists, a bitter scientific dispute arose between them, and this unfortunately led to

#469530