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📚📚
Post-Tensioned Box Girder Design Manual
hif150-2016
This manual presents design methodologies for cast-in-place concrete box girder bridges post-tensioned with internal post-tensioning tendons, within the framework of the AASHTO LRFD Bridge Design Specifications (2012).
http://www.mediafire.com/file/0etkyf5hm3lg3ut/hif15016.pdf/file
📚📚
Post-Tensioned Box Girder Design Manual
hif150-2016
This manual presents design methodologies for cast-in-place concrete box girder bridges post-tensioned with internal post-tensioning tendons, within the framework of the AASHTO LRFD Bridge Design Specifications (2012).
http://www.mediafire.com/file/0etkyf5hm3lg3ut/hif15016.pdf/file
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Precast Prestressed Concrete Piles
https://www.mediafire.com/file/me7tjs2i0rvr3ko/Prestressed+Concrete+Piles.pdf/file
Precast Prestressed Concrete Piles
https://www.mediafire.com/file/me7tjs2i0rvr3ko/Prestressed+Concrete+Piles.pdf/file
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كمرة خرسانية مسبقة الصب و مسبقة الإجهاد
بنظام الشد السابق .
Huge Prestressed Concrete Girder.
كمرة خرسانية مسبقة الصب و مسبقة الإجهاد
بنظام الشد السابق .
Huge Prestressed Concrete Girder.
#PSC_TECH
يعتبر المهندس الصيني
Tung Yen Lin (1912-2003)
خليفة للمهندس الفرنسي
Eugene Freyssinet
حيث أبدع في تصميم المنشآت الخرسانية مسبقة الإجهاد .
نترككم مع نبذة عن حياته و إنجازاته في المقال التالي :
Tung Yen Lin, a professor emeritus in civil engineering at the University of California, Berkeley, considered one of the greatest structural engineers of his time, Lin earned a reputation for combining elegance and strength in his designs. Evidence of Lin's work can be seen worldwide, from San Francisco's Moscone Convention Center to the Kuan Du Bridge in Taiwan to the roof of the National Racetrack in Venezuela.
Born in Fuzhou, China, on Nov. 14, 1912, Lin was the fourth of 11 children. He was raised in Beijing, where his father moved the family when he joined China's Supreme Court.
Educated at home until he was 11, Lin did not begin formal schooling until junior high school. Lin was too young at the time to enroll, but his parents said he was born in 1911 instead of 1912, a fib that to this day is reflected in some of Lin's personnel records.
Despite a semi-rough transition into the school system - Lin flunked out of history the first year - he recovered quickly and discovered a strong aptitude for calculations. Three years later, when he was only 14, he passed the college entrance exams, earning the top score in math and the second best score overall in his entering class at Jiaotong University's Tangshan Engineering College, which he entered in 1926.
In 1931, at the age of 19, Lin earned his bachelor's degree in civil engineering from the college. He then left for the United States and began his graduate studies at UC Berkeley. Early in his career, Lin gained recognition in his field with his master's thesis on direct moment distribution. The innovative paper advanced structural analysis and was the first student thesis published by the American Society of Civil Engineers.
After receiving his UC Berkeley master's degree in civil engineering in 1933, Lin returned to China to work with the Chinese Ministry of Railways. He quickly moved up the ranks, becoming chief bridge engineer of the Yunnan-Chongqing Railway four years later at the age of 25. In his position, Lin oversaw the survey, design and construction of more than 1,000 bridges throughout China's mountainous regions.
In 1946, while Lin was working in Taiwan to help in the transition from Japanese to Chinese rule after the end of World War II, he accepted an invitation to join UC Berkeley's faculty.
It was here that Lin began his groundbreaking research in prestressed concrete, dramatically simplifying the design process for using the material, which combines the tensile strength of steel wires with the compressive strength of concrete. Colleagues said the research on prestressed concrete spearheaded by Lin was key to popularizing the material, which was relatively unknown in the United States at the time.
Lin believed so strongly in the material that he helped assemble in San Francisco in the summer of 1957 the first World Conference on Prestressed Concrete, which was attended by 1,200 engineers, scientists and manufacturers.
"The results of this international gathering, coupled with T.Y.'s pioneering work to perfect the use of prestressed concrete, changed the history of building, making possible today's high-rises and graceful long-span structures that can bear heavy loads, withstand earthquakes and hurricanes and cost little to maintain," said Scordelis, Lin's former colleague, in an introduction to an oral history interview of Lin prepared by the Regional Oral History Office at UC Berkeley's Bancroft Library.
It was in the midst of the Cold War that Lin developed one of his boldest ideas: Connecting Alaska to Siberia with a bridge across the Bering Strait. He called the proposed structure the "Intercontinental Peace Bridge" because he saw the span as a critical link that could foster better relations between the United States and Russia.
يعتبر المهندس الصيني
Tung Yen Lin (1912-2003)
خليفة للمهندس الفرنسي
Eugene Freyssinet
حيث أبدع في تصميم المنشآت الخرسانية مسبقة الإجهاد .
نترككم مع نبذة عن حياته و إنجازاته في المقال التالي :
Tung Yen Lin, a professor emeritus in civil engineering at the University of California, Berkeley, considered one of the greatest structural engineers of his time, Lin earned a reputation for combining elegance and strength in his designs. Evidence of Lin's work can be seen worldwide, from San Francisco's Moscone Convention Center to the Kuan Du Bridge in Taiwan to the roof of the National Racetrack in Venezuela.
Born in Fuzhou, China, on Nov. 14, 1912, Lin was the fourth of 11 children. He was raised in Beijing, where his father moved the family when he joined China's Supreme Court.
Educated at home until he was 11, Lin did not begin formal schooling until junior high school. Lin was too young at the time to enroll, but his parents said he was born in 1911 instead of 1912, a fib that to this day is reflected in some of Lin's personnel records.
Despite a semi-rough transition into the school system - Lin flunked out of history the first year - he recovered quickly and discovered a strong aptitude for calculations. Three years later, when he was only 14, he passed the college entrance exams, earning the top score in math and the second best score overall in his entering class at Jiaotong University's Tangshan Engineering College, which he entered in 1926.
In 1931, at the age of 19, Lin earned his bachelor's degree in civil engineering from the college. He then left for the United States and began his graduate studies at UC Berkeley. Early in his career, Lin gained recognition in his field with his master's thesis on direct moment distribution. The innovative paper advanced structural analysis and was the first student thesis published by the American Society of Civil Engineers.
After receiving his UC Berkeley master's degree in civil engineering in 1933, Lin returned to China to work with the Chinese Ministry of Railways. He quickly moved up the ranks, becoming chief bridge engineer of the Yunnan-Chongqing Railway four years later at the age of 25. In his position, Lin oversaw the survey, design and construction of more than 1,000 bridges throughout China's mountainous regions.
In 1946, while Lin was working in Taiwan to help in the transition from Japanese to Chinese rule after the end of World War II, he accepted an invitation to join UC Berkeley's faculty.
It was here that Lin began his groundbreaking research in prestressed concrete, dramatically simplifying the design process for using the material, which combines the tensile strength of steel wires with the compressive strength of concrete. Colleagues said the research on prestressed concrete spearheaded by Lin was key to popularizing the material, which was relatively unknown in the United States at the time.
Lin believed so strongly in the material that he helped assemble in San Francisco in the summer of 1957 the first World Conference on Prestressed Concrete, which was attended by 1,200 engineers, scientists and manufacturers.
"The results of this international gathering, coupled with T.Y.'s pioneering work to perfect the use of prestressed concrete, changed the history of building, making possible today's high-rises and graceful long-span structures that can bear heavy loads, withstand earthquakes and hurricanes and cost little to maintain," said Scordelis, Lin's former colleague, in an introduction to an oral history interview of Lin prepared by the Regional Oral History Office at UC Berkeley's Bancroft Library.
It was in the midst of the Cold War that Lin developed one of his boldest ideas: Connecting Alaska to Siberia with a bridge across the Bering Strait. He called the proposed structure the "Intercontinental Peace Bridge" because he saw the span as a critical link that could foster better relations between the United States and Russia.
For Lin, bridges had become the tangible symbol of his desire to not only connect two bodies of land, but to span cultures and politics.
"Psychologically, this bridge will demonstrate that human energy and technical capabilities can be devoted to constructive rather than destructive measures to the benefit of all mankind," wrote Lin in a statement describing the project's mission.
Lin's dream made its way to the White House when, in 1986, President Ronald Reagan presented Lin with the prestigious National Medal of Science, the country's highest scientific honor. Lin took the opportunity to hand the president a 16-page booklet outlining plans for the 50-mile span and give him a quick pitch on the bridge's merits, a move that made news around the world. The proposed bridge, which drew both raves and criticism, still remains on paper.
Lin proposed other daring projects such as a 9-mile bridge connecting Spain and Morocco across the Strait of Gibraltar. If built, the span would have become the world's longest suspension bridge.
In the Bay Area, Lin's expertise influenced the design of the San Mateo Bridge, as well as the Interstate 80 bridge in Berkeley for pedestrians and bicyclists designed by OPAC Consulting Engineers. He worked with Mark Ketchum, vice president of the firm and a UC Berkeley graduate. Ketchum was one of Lin's former teaching assistants and a longtime professional colleague.
Lin was also a member of the California Department of Transportation advisory panel on the new eastern span of the Bay Bridge. As a member, Lin criticized the single tower suspension design that slated for construction.
In 1954, Lin founded the firm T.Y. Lin and Associates to help move prestressed concrete from the realm of research into real-world applications. The firm's name changed to T.Y. Lin International by the late 1960s to reflect the company's growth and worldwide presence.
During Lin's tenure at UC Berkeley, he served as chair of the Division of Structural Engineering and Structural Mechanics and as director of the Structural Engineering Laboratory from 1960 to 1963. He was appointed campus-wide Professor of Arts and Science for the 1968-69 academic year to advance interdisciplinary teaching. And from 1969-70, during a turbulent time on campus, Lin chaired UC Berkeley's Board of Educational Development.
He retired from UC Berkeley in 1976 to lead T.Y. Lin International full-time. He left the firm in 1992, five years after it had been sold and went on to form San Francisco-based Lin Tung-Yen China, Inc., which focuses on various engineering projects in China. Lin's son-in-law, Robert Yee, is president of that company.
Lin took particular pride in the role he played in influencing the redevelopment of Pudong, an island off the coast of Shanghai that had been full of old factories and farmland, said Yee. Taking a cue from capitalism, Lin suggested that land be leased in Pudong to pay for bridges linking the island to Shanghai. The idea of building bridges to Pudong and redeveloping the region eventually won favor with city and national officials, including former Chinese President Jiang Zemin, who was mayor of Shanghai when Lin worked with him. The plan was approved in 1989 by Deng Xiaoping, the senior leader of China at the time. There are now 10 bridges or tunnels between Shanghai and Pudong, and six more are being planned.
One of the last projects Lin worked on was the Nanning Bridge in Nanning, China. Working with Ketchum at OPAC, Lin helped design a unique asymmetrical arched bridge on a curve. Expected to be completed by the end of 2004, the span will be the only one of its kind.
In addition to the National Medal of Science, Lin received numerous honors throughout his career, including a Fulbright Award for study in Belgium in 1953 and election to the National Academy of Engineering in 1967. He was the first recipient of the American Society of Civil Engineers' Outstanding Lifetime Achievement in Design award. The society renamed its annual Prestressed Concrete Award the T.Y. Lin Award.
"Psychologically, this bridge will demonstrate that human energy and technical capabilities can be devoted to constructive rather than destructive measures to the benefit of all mankind," wrote Lin in a statement describing the project's mission.
Lin's dream made its way to the White House when, in 1986, President Ronald Reagan presented Lin with the prestigious National Medal of Science, the country's highest scientific honor. Lin took the opportunity to hand the president a 16-page booklet outlining plans for the 50-mile span and give him a quick pitch on the bridge's merits, a move that made news around the world. The proposed bridge, which drew both raves and criticism, still remains on paper.
Lin proposed other daring projects such as a 9-mile bridge connecting Spain and Morocco across the Strait of Gibraltar. If built, the span would have become the world's longest suspension bridge.
In the Bay Area, Lin's expertise influenced the design of the San Mateo Bridge, as well as the Interstate 80 bridge in Berkeley for pedestrians and bicyclists designed by OPAC Consulting Engineers. He worked with Mark Ketchum, vice president of the firm and a UC Berkeley graduate. Ketchum was one of Lin's former teaching assistants and a longtime professional colleague.
Lin was also a member of the California Department of Transportation advisory panel on the new eastern span of the Bay Bridge. As a member, Lin criticized the single tower suspension design that slated for construction.
In 1954, Lin founded the firm T.Y. Lin and Associates to help move prestressed concrete from the realm of research into real-world applications. The firm's name changed to T.Y. Lin International by the late 1960s to reflect the company's growth and worldwide presence.
During Lin's tenure at UC Berkeley, he served as chair of the Division of Structural Engineering and Structural Mechanics and as director of the Structural Engineering Laboratory from 1960 to 1963. He was appointed campus-wide Professor of Arts and Science for the 1968-69 academic year to advance interdisciplinary teaching. And from 1969-70, during a turbulent time on campus, Lin chaired UC Berkeley's Board of Educational Development.
He retired from UC Berkeley in 1976 to lead T.Y. Lin International full-time. He left the firm in 1992, five years after it had been sold and went on to form San Francisco-based Lin Tung-Yen China, Inc., which focuses on various engineering projects in China. Lin's son-in-law, Robert Yee, is president of that company.
Lin took particular pride in the role he played in influencing the redevelopment of Pudong, an island off the coast of Shanghai that had been full of old factories and farmland, said Yee. Taking a cue from capitalism, Lin suggested that land be leased in Pudong to pay for bridges linking the island to Shanghai. The idea of building bridges to Pudong and redeveloping the region eventually won favor with city and national officials, including former Chinese President Jiang Zemin, who was mayor of Shanghai when Lin worked with him. The plan was approved in 1989 by Deng Xiaoping, the senior leader of China at the time. There are now 10 bridges or tunnels between Shanghai and Pudong, and six more are being planned.
One of the last projects Lin worked on was the Nanning Bridge in Nanning, China. Working with Ketchum at OPAC, Lin helped design a unique asymmetrical arched bridge on a curve. Expected to be completed by the end of 2004, the span will be the only one of its kind.
In addition to the National Medal of Science, Lin received numerous honors throughout his career, including a Fulbright Award for study in Belgium in 1953 and election to the National Academy of Engineering in 1967. He was the first recipient of the American Society of Civil Engineers' Outstanding Lifetime Achievement in Design award. The society renamed its annual Prestressed Concrete Award the T.Y. Lin Award.
In 1976, Lin received the Berkeley Citation, one of the campus's most distinguished honors, and in 1994, was named UC Berkeley's California Alumnus of the Year.
Lin also contributed more than 100 technical and research papers and co-authored three widely used textbooks in structural engineering.
T.Y. Lin died Saturday, Nov. 15, 2003
at his El Cerrito home after a fall resulting from a mild heart attack. He had remained active throughout his life, having met with former students and worked at his San Francisco office the week before his death.
Lin also contributed more than 100 technical and research papers and co-authored three widely used textbooks in structural engineering.
T.Y. Lin died Saturday, Nov. 15, 2003
at his El Cerrito home after a fall resulting from a mild heart attack. He had remained active throughout his life, having met with former students and worked at his San Francisco office the week before his death.
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Tung Yen Lin (1912-2003)
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LOAD BALANCING AS A DESIGN TOOL
Load balancing was first introduced by T.Y. Lin as an alternative method for analyzing prestressed members. This powerful method provides a simple process for checking presstressed members using hand calculations. This method of analysis seeks to remove the presstressing stands from the structural member and replace them with a set of equivalent forces that act on the member.
In traditional design, the equivalent forces act in a direction that is opposite the applied loading on the member – it is possible to “balance” a portion of the applied loads with equivalent prestress forces, sometimes referred to as the “balanced load” as referenced in Figure 1.
Experienced engineers recommend checking the balanced dead load percentage during design of a member as this can provide insight into the efficiency and reliability of the design. Balanced loads exceeding 100% dead load are often acceptable and even desirable, as long as the design is serviceable and code-compliant. There is no specific code requirement on the percentage of load that should be balanced with post-tensioning, and we do not recommend using a prescribed percentage as a design criterion.
We have often seen instances where designers have attempted to balance more than 300% of the dead load in some spans – this is a sure bet for failure during stressing. For transfer members such as transfer girders, transfer plates, and podium slabs, it is not unusual to have balanced loads that exceed 150% of the dead load. These cases can be complex and it is vital that the engineering team pay close attention to initial stresses, service load stresses, initial and long-term deflections, and detailing of reinforcing steel. In many transfer members; it is necessary to stage stress by stressing the member at successive intervals as load is being added to the member.
Just as overbalancing may be an indicator that the slab or beam does not have adequate thickness or depth, under-balancing may be an indicator that the member depth is overly conservative. Again, checking the percentage of dead load that is balanced is an important tool that should be used to refine and verify the design.
For typical slabs in buildings, we recommend using the values in Table 1.
In our experience, the load balancing method of analysis is perhaps the most powerful tool at the disposal of an engineer who designs prestressed structures.
While reliance on computer software for design of prestressed concrete members is nearly universal, it is possible to design these members using hand calculations. After all, this is how buildings were designed before the proliferation of computers. It is important for the design engineer to be able to perform hand calculations to check a design or even to make a last minute tendon adjustment in the field before a pour. So how is this possible? The answer lies in the load balancing method together with Equation 1 :
Wpre= ( 8 × P × a ) / ( 12 × I^2 )
Where:
Wpre is the balanced load due to prestress
P is prestress force
l is span length
a is tendon drape defined in the figure
Equation 1 defines the relationship between prestress force (P), tendon drape (a), and balanced load (Wpre), and is based on the assumption of an idealized parabolic tendon profile. If any 2 of these variables is known, then the third can be calculated using this equation.
For example, it is possible to determine the tendon force for a design strip in a two-way slab with tributary width of 20 ft, span length of 30 ft, slab thickness of 8 in, and the assumption that the post-tensioning should balance 80 percent of the self-weight of the slab.
Wpre= 0.8 x 8 x 0.15 x 20 /12
= 1.6 k/ft
l = 30 ft
LOAD BALANCING AS A DESIGN TOOL
Load balancing was first introduced by T.Y. Lin as an alternative method for analyzing prestressed members. This powerful method provides a simple process for checking presstressed members using hand calculations. This method of analysis seeks to remove the presstressing stands from the structural member and replace them with a set of equivalent forces that act on the member.
In traditional design, the equivalent forces act in a direction that is opposite the applied loading on the member – it is possible to “balance” a portion of the applied loads with equivalent prestress forces, sometimes referred to as the “balanced load” as referenced in Figure 1.
Experienced engineers recommend checking the balanced dead load percentage during design of a member as this can provide insight into the efficiency and reliability of the design. Balanced loads exceeding 100% dead load are often acceptable and even desirable, as long as the design is serviceable and code-compliant. There is no specific code requirement on the percentage of load that should be balanced with post-tensioning, and we do not recommend using a prescribed percentage as a design criterion.
We have often seen instances where designers have attempted to balance more than 300% of the dead load in some spans – this is a sure bet for failure during stressing. For transfer members such as transfer girders, transfer plates, and podium slabs, it is not unusual to have balanced loads that exceed 150% of the dead load. These cases can be complex and it is vital that the engineering team pay close attention to initial stresses, service load stresses, initial and long-term deflections, and detailing of reinforcing steel. In many transfer members; it is necessary to stage stress by stressing the member at successive intervals as load is being added to the member.
Just as overbalancing may be an indicator that the slab or beam does not have adequate thickness or depth, under-balancing may be an indicator that the member depth is overly conservative. Again, checking the percentage of dead load that is balanced is an important tool that should be used to refine and verify the design.
For typical slabs in buildings, we recommend using the values in Table 1.
In our experience, the load balancing method of analysis is perhaps the most powerful tool at the disposal of an engineer who designs prestressed structures.
While reliance on computer software for design of prestressed concrete members is nearly universal, it is possible to design these members using hand calculations. After all, this is how buildings were designed before the proliferation of computers. It is important for the design engineer to be able to perform hand calculations to check a design or even to make a last minute tendon adjustment in the field before a pour. So how is this possible? The answer lies in the load balancing method together with Equation 1 :
Wpre= ( 8 × P × a ) / ( 12 × I^2 )
Where:
Wpre is the balanced load due to prestress
P is prestress force
l is span length
a is tendon drape defined in the figure
Equation 1 defines the relationship between prestress force (P), tendon drape (a), and balanced load (Wpre), and is based on the assumption of an idealized parabolic tendon profile. If any 2 of these variables is known, then the third can be calculated using this equation.
For example, it is possible to determine the tendon force for a design strip in a two-way slab with tributary width of 20 ft, span length of 30 ft, slab thickness of 8 in, and the assumption that the post-tensioning should balance 80 percent of the self-weight of the slab.
Wpre= 0.8 x 8 x 0.15 x 20 /12
= 1.6 k/ft
l = 30 ft
a = 8 – 1 – 1= 6 in
P = 12 × Wpre × ( l^2 / 8 × a) = 360 kips
Equation 1 provides a simple and elegant way to perform preliminary design or to check a design to ensure that it is reasonable. Clearly, once the tendon force and profile are established, the design must be checked against all of the serviceability and strength requirements in the code. But it can be shown that for members that are sized using customary span-to-depth ratios and that are subjected to typical superimposed dead and live loads, equation 1 will provide a reasonable solution. Be advised, however, that this equation does not apply for cantilevers or for spans with harped tendons. Also, it is not advisable to use Equation 1 for designing transfer members, including podium slabs.
As can be seen in the example above, Equation 1 is one of the most useful tools at the disposal of engineer designing post-tensioned concrete.
P = 12 × Wpre × ( l^2 / 8 × a) = 360 kips
Equation 1 provides a simple and elegant way to perform preliminary design or to check a design to ensure that it is reasonable. Clearly, once the tendon force and profile are established, the design must be checked against all of the serviceability and strength requirements in the code. But it can be shown that for members that are sized using customary span-to-depth ratios and that are subjected to typical superimposed dead and live loads, equation 1 will provide a reasonable solution. Be advised, however, that this equation does not apply for cantilevers or for spans with harped tendons. Also, it is not advisable to use Equation 1 for designing transfer members, including podium slabs.
As can be seen in the example above, Equation 1 is one of the most useful tools at the disposal of engineer designing post-tensioned concrete.