Bridges are structures which carry people and vehicles across natural or man-made obstacles. As early roads connected villages and towns, people traveled by foot or with carts and wagons. Although a person carrying a large bundle might be able to cross a stream by swimming or stepping on stones, as horse drawn vehicles with heavy loads needed to cross more dangerous terrain, permanent sturdy bridges became an important part of transportation systems.
Early bridges were made from local materials such as wood, stone and fibers. Today, most bridges have a concrete, steel, or wood framework with an asphalt or concrete roadway. Based on the length of the barrier to be crossed, the amount and type of traffic as well as forces of nature (wind, tide, flood) different materials and shapes of bridges are used.
There are many types of bridges such as arch bridges, girder bridges, truss bridges, cantilever bridges, cable-stayed bridges, suspension bridges and moveable bridges. Many bridges are actually combinations of different types of bridges -- and no two bridges are identical! Most bridges are held up by at least two supports set in the ground called abutments. Some bridges have additional supports along the middle of the bridge called piers. A span is the distance between two supports, either two piers, a pier and an abutment or two abutments. Many short bridges are supported only by the abutments and are called single-span bridges. Longer bridges usually have one or more piers to support them and are known as multi-span bridges.
How Bridges Work
Most machines do some type of work. You know an engine, windmill or other machine is generating a force or work because you can see the motion. Although a bridge does not have spinning moving parts like other machines, it is still doing work.
What is a bridge's work? A bridge needs to be strong enough to support its own weight plus the load of passengers and vehicles travelling on it against the pull of gravity. A bridge works against the pull of gravity. If you hold a facial tissue between your hands and place a heavy book on top of a facial tissue, you know the book will break through the tissue. The tissue is not strong enough to support the weight of the book.
How do bridge's work? Although there are many types of bridges most bridges work by balancing compression and tension. Place a flexible object like an eraser, sponge, or small piece of bread between your thumb and index finger. Press your fingers together. One side of the object will bend inwards and shorten while the other will bend outwards and lengthen. The shorter side has been compressed, while the other side is under tension. Bridge components experience these tension and compression stresses.
Bridge materials, like stone, wood, steel and concrete, all have different strengths. For example, steel can be much stronger than wood. Some materials are easier to form a particular shape. Different materials can withstand different amounts of compression and tension. For example, stone can withstand a lot of compression, but under a lot of tension will break. Steel is very flexible and can endure a lot more compression and tension then materials like iron, wood or stone. Engineers will select materials and a bridge design, based on the strength of the material, amount and type of stress a material can withstand and other bridge requirements (length, terrain, etc.).
Different Types Of Bridges
Arch bridges are structures in which each span forms an arch. The arch bridge is one of the oldest types of bridges. Early arch bridges were made from stone. The spans range up to about 1700 ft.
Girder bridges are made of beams called girders. The ends of the beams or girders rest on piers or abutments. The span length of girder bridges ranges up to about 1000 ft
Truss bridges are supported by frameworks called trusses. Trusses are beams arranged to form triangles
Cantilever bridges consist of two independent beams, cantilevers, that extend from opposite banks of a waterway. Cantilever bridges have spans as long at 1800 ft
Cable-stayed bridges have roadways that hang from cables. The cables are connected directly to towers.
Moveable bridges have roadway that is moved to provide enough clearance for boats or large ships to pass. An example of a moveable bridge is a drawbridge that tilts the roadway upward
Suspension bridges may be the most impressive type of bridge with their long main span and beauty. These bridges have a roadway that hangs from steel cables supported by two high towers. The difference between suspension bridges and cable-stayed bridges is that suspension bridge cables are not directly connected to the towers. The cables of a suspension bridge are not connected to the bridge - the cables pass through a hole in the top of the towers.
A suspension bridge has at least two main cables. These cables extend from one end of the bridge to the other. Suspender cables hang from these main cables. The other end of the suspender attaches to the roadway.
Wednesday, 7 January 2009
Cement Standards and Specifications
Cement Standards and Specifications
Concrete Technology Home > Cement Basics > Cement standards and specifications
Standards Organizations
Product specifications and test methods are typically developed by national standards development organizations, such as ASTM in the U.S. and CSA in Canada. Full consensus standards are developed with the participation of all parties who have a stake in the standards’ development and/or use. The table below lists the most relevant national and international standard organizations for the concrete industry. U.S. and Canada
ASTM ASTM International. Has a history of more than 100 years of standards development activities, including the first national specifications for portland cement and other concrete materials. Uses a consensus-based standards development process. Committee C01 develops standards related to hydraulic cements and Committee C09 develops standards for concrete and other concrete materials.
AASHTO American Association of State Highway and Transportation Officials. Develops standards for many materials though participation of state departments of transportation staff. AASHTO’s Subcommittee on Materials develops concrete-related specifications, many of which are closely related to ASTM standards.
CSA Canadian Standards Association. Develops standards for use in Canada through a consensus process, including the CSA A3000 compendium on cementitious materials.
International
ISO International Organization for Standardization. Cement-related standards are developed by TC (Technical Committee) 74 (Cement and Lime) and concrete-related standards by TC 71 (Concrete, reinforced concrete and pre-stressed concrete).
CEN European Committee for Standardization. EN 197 is the standard specification for cement in CEN member countries and EN 206 is the standard specification for concrete.
Product specifications and test methods are referenced in local and international building codes and specifications for ease of reference. Click here for information on building codes and standards. For concrete construction projects, other organizations, such as state DOTs or the FAA, also develop specifications that typically refer to ASTM or AASHTO specifications.
Cement Specifications
Different types of cement are manufactured to meet various physical and chemical requirements. There are currently three different common hydraulic cement standards for general concrete construction in use in the U.S.:
ASTM C150 (AASHTO M 85), Specification for Portland Cement
ASTM C595 (AASHTO M 240), Specification for Blended Hydraulic Cements
ASTM C1157, Performance Specification for Hydraulic Cements
Each of these three specifications provides for several different types of cement. The table below provides a matrix of these types and where they are used in concrete construction:
Applications of Commonly Used Cements
Cement Specification Applications*
General purpose Moderate heat of hydration High early strength Low heat of hydration Moderate sulfate resistance High sulfate resistance Resistance to alkali-silica reactivity (ASR)**
ASTM C150
(AASHTO M 85) portland cements I II (moderate heat option) III IV II V Low alkali option
ASTM C595
(AASHTO M 240) blended hydraulic cements IS
IP IS(<70)(MH)
IP(MH)
- IP(LH) IS(<70)(MS)
IP(MS) IS(<70)(HS)
IP(HS) Low reactivity option
ASTM C1157 hydraulic cements*** GU MH HE LH MS HS Option R
*Check the availability of specific cements as all cements are not available everywhere.
**The option for low reactivity with ASR susceptible aggregates can be applied to any cement type in the columns to the left.
*** For ASTM C1157 cements, the nomenclature of hydraulic cement, portland cement, air-entraining portland cement, modified portland cement, or blended hyraulic cement is used with the type designation.
Click here for more details on specifying cements for use in concrete and on how to determine which cement might be most appropriate for your construction needs.
Click here for more information on masonry cement standards.
ASTM/AASHTO Harmonization
AASHTO M 85 and ASTM C150 have existed as parallel standards for portland cement since the 1940s. U.S. state departments of transportation reference either AASHTO M 85 or ASTM C150 when specifying portland cement for concrete construction. While the provisions of AASHTO M 85 and ASTM C150 have generally been consistent, there have also been some substantive differences. In the summer of 2003, a dialog between the two organizations was established with the goal of developing improvements to both specifications and harmonizing the differences between them. Several harmonized provisions have already been adopted by both organizations. Harmonization efforts continue in order to develop provisions that meet collective needs, and to develop mechanisms for implementing improvements to cement standards.
ASTM Specification C10 for Natural Cement
Natural cements were extensively used in 19th and early 20th century construction, and many historic structures were built with these materials. However, with improved technology for producing portland cements, sales of natural cements began to decline in the late 1800s, stopping entirely by the mid-1970s.
To meet the needs of architects, engineers, and historians working on restoration projects, natural cement production has begun again in the U.S. and a specification was needed to define the product. ASTM International has reissued an updated ASTM C10, Specification for Natural Cement, to fill that need. .
Concrete Technology Home > Cement Basics > Cement standards and specifications
Standards Organizations
Product specifications and test methods are typically developed by national standards development organizations, such as ASTM in the U.S. and CSA in Canada. Full consensus standards are developed with the participation of all parties who have a stake in the standards’ development and/or use. The table below lists the most relevant national and international standard organizations for the concrete industry. U.S. and Canada
ASTM ASTM International. Has a history of more than 100 years of standards development activities, including the first national specifications for portland cement and other concrete materials. Uses a consensus-based standards development process. Committee C01 develops standards related to hydraulic cements and Committee C09 develops standards for concrete and other concrete materials.
AASHTO American Association of State Highway and Transportation Officials. Develops standards for many materials though participation of state departments of transportation staff. AASHTO’s Subcommittee on Materials develops concrete-related specifications, many of which are closely related to ASTM standards.
CSA Canadian Standards Association. Develops standards for use in Canada through a consensus process, including the CSA A3000 compendium on cementitious materials.
International
ISO International Organization for Standardization. Cement-related standards are developed by TC (Technical Committee) 74 (Cement and Lime) and concrete-related standards by TC 71 (Concrete, reinforced concrete and pre-stressed concrete).
CEN European Committee for Standardization. EN 197 is the standard specification for cement in CEN member countries and EN 206 is the standard specification for concrete.
Product specifications and test methods are referenced in local and international building codes and specifications for ease of reference. Click here for information on building codes and standards. For concrete construction projects, other organizations, such as state DOTs or the FAA, also develop specifications that typically refer to ASTM or AASHTO specifications.
Cement Specifications
Different types of cement are manufactured to meet various physical and chemical requirements. There are currently three different common hydraulic cement standards for general concrete construction in use in the U.S.:
ASTM C150 (AASHTO M 85), Specification for Portland Cement
ASTM C595 (AASHTO M 240), Specification for Blended Hydraulic Cements
ASTM C1157, Performance Specification for Hydraulic Cements
Each of these three specifications provides for several different types of cement. The table below provides a matrix of these types and where they are used in concrete construction:
Applications of Commonly Used Cements
Cement Specification Applications*
General purpose Moderate heat of hydration High early strength Low heat of hydration Moderate sulfate resistance High sulfate resistance Resistance to alkali-silica reactivity (ASR)**
ASTM C150
(AASHTO M 85) portland cements I II (moderate heat option) III IV II V Low alkali option
ASTM C595
(AASHTO M 240) blended hydraulic cements IS
IP IS(<70)(MH)
IP(MH)
- IP(LH) IS(<70)(MS)
IP(MS) IS(<70)(HS)
IP(HS) Low reactivity option
ASTM C1157 hydraulic cements*** GU MH HE LH MS HS Option R
*Check the availability of specific cements as all cements are not available everywhere.
**The option for low reactivity with ASR susceptible aggregates can be applied to any cement type in the columns to the left.
*** For ASTM C1157 cements, the nomenclature of hydraulic cement, portland cement, air-entraining portland cement, modified portland cement, or blended hyraulic cement is used with the type designation.
Click here for more details on specifying cements for use in concrete and on how to determine which cement might be most appropriate for your construction needs.
Click here for more information on masonry cement standards.
ASTM/AASHTO Harmonization
AASHTO M 85 and ASTM C150 have existed as parallel standards for portland cement since the 1940s. U.S. state departments of transportation reference either AASHTO M 85 or ASTM C150 when specifying portland cement for concrete construction. While the provisions of AASHTO M 85 and ASTM C150 have generally been consistent, there have also been some substantive differences. In the summer of 2003, a dialog between the two organizations was established with the goal of developing improvements to both specifications and harmonizing the differences between them. Several harmonized provisions have already been adopted by both organizations. Harmonization efforts continue in order to develop provisions that meet collective needs, and to develop mechanisms for implementing improvements to cement standards.
ASTM Specification C10 for Natural Cement
Natural cements were extensively used in 19th and early 20th century construction, and many historic structures were built with these materials. However, with improved technology for producing portland cements, sales of natural cements began to decline in the late 1800s, stopping entirely by the mid-1970s.
To meet the needs of architects, engineers, and historians working on restoration projects, natural cement production has begun again in the U.S. and a specification was needed to define the product. ASTM International has reissued an updated ASTM C10, Specification for Natural Cement, to fill that need. .
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