What Is a Girder Bridge?

Beam Bridge A bridge with a main beam that is mainly bent as a load-bearing member. The main beam can be a solid web beam or a truss beam. The solid web beam has a simple structure and is relatively easy to manufacture, erection and maintenance. It is widely used in medium and small span bridges, but it is not economical in terms of material utilization. The members of the truss beams bear axial forces, the materials can be fully utilized, their weight is light, and their spanning capacity is large, and they are mostly used to build long-span bridges. According to the static system of the main beam, it is divided into simple supported beam bridge, continuous beam bridge and cantilever beam bridge.

Bridges with beams as the main load-bearing members are the earliest bridge types in China and have been created since the Yin Dynasty. The most primitive girder bridge was a single-wood bridge, which developed into several bamboo and wooden juxtapositions. Since then, the beam bridge has continued to evolve, replacing stone and bamboo with materials in terms of materials, and gradually developing and innovating in terms of structure. Auxiliary boom beam bridges, splay beam bridges and outrigger beam bridge structures have emerged. The bridge developed into a porous beam bridge. The support of the porous beam bridge generally uses wooden pillars, stone pillars or stone piers, and cast iron pillars are also used. Due to the simple structure and easy construction of the beam bridge, especially the stone beam bridge is durable and requires less labor for maintenance, it has become the most common bridge type. Existing large-scale ancient stone girder bridges are concentrated in the coastal areas of Fujian, especially in Quanzhou. Well-known are Wan'an Bridge (commonly known as Luoyang Bridge) and Anping Bridge (commonly known as Wuli Bridge). Most of these bridges were built during the Song and Yuan dynasties. They were mainly constructed using raft-type foundations, spike-shaped piers, and huge floating beams. Some bridges also cleverly used the breeding characteristics of sea oysters to strengthen the bridge foundation and Bridge pier. These process technologies are major breakthroughs and innovations in the history of bridge construction, and they are also the first in the history of bridge construction in the world. ^[1]

The superstructure is a bridge consisting of main load-bearing beams that are simply supported on the piers at both ends. The simply supported beam is a statically determinate structure. The adjacent spans are individually stressed, and the structure is relatively simple. It is not affected by the displacement of the support. It is suitable for various geological conditions. The structure is relatively simple, and it is easy to be standardized and assembled. The component is more convenient to manufacture and install. It is the most widely used beam bridge. However, the mid-span bending moment of a simply supported beam will increase sharply with the increase of the span, so it appears uneconomical at large spans. ^[2]

The superstructure consists of beams spanning more than three bearings as bridges for the main load-bearing structure. Under constant load, the maximum positive bending moment in the span is significantly reduced due to the unloading effect of the negative moment at the fulcrum, so it will be more economical to use a simple-supported beam bridge with a larger span. The continuous beam only needs to have a support on each pier, the bridge pier width is small, saving material; and the beam continuously passes through the support, there are fewer joints, and the traffic is smooth, so it is beneficial to high-speed driving. However, the continuous beam is a statically indeterminate structure, and the displacement of the support will cause the internal force of the structure to change. It is suitable for bridges with good geology. It can be built with reinforced concrete, prestressed concrete and steel. ^[2]

The upper structure consists of anchor holes, cantilevers and suspension holes. The suspension holes are supported on the cantilever and are linked by hinges. There are single cantilever beam bridges (three-span construction, large mid-span to meet navigation requirements) and double cantilever beam bridges (can form multi-span long beam bridges). For example, the Xianyang Weihe Bridge in Shaanxi Province (a main span of 174 meters, a total length of 448 meters, completed in 1954) is a reinforced concrete cantilever bridge. Girder bridges are one of the basic systems of bridges. They are widely used and occupy a large proportion in bridge construction. Their superstructures can be wooden structures, steel structures, reinforced concrete structures, prestressed concrete structures, or reinforced concrete bridge decks and steel beams. Composite Structure.

Beam Bridge Historic Bridge

The Weishui Third Bridge, located near the ancient city of Xianyang, was famous in ancient times. The three bridges include Zhongwei, East Wei and West Wei bridges, all of which are multi-span wooden beams and wooden pillar bridges. Among them, the Zhongwei Bridge was built at the time of King Qin Zhao of the Warring States Period, and later Qin Shihuang rebuilt and strengthened it. The bridge is approximately 525 meters in length and 13.8 meters in width, which is close to the width of the Nanjing Yangtze River Bridge driveway. It consists of 750 wooden pillar piles and 67 bridge piers and 68 bridge holes. The diameter is nine meters; the top beams are covered on the wooden pillar piles to form the piers, and then the large wooden beams are laid on the trusses, and then the wooden bridge deck is laid. The middle bridge hole is high and large, and the bridge holes on both sides are low and small. At both ends of the bridge are also erected huabiao, Zhenshui demon stone pieces, stone lampposts, etc. for display and lighting. In the Han Dynasty, the Zhongwei Bridge was rebuilt, and the East and West Weiqiao were added.

Beam bridges during the Han Dynasty have become relatively popular. The portrait of the Han Tomb unearthed in Yinan, Shandong Province has even been engraved with the pattern of a stone beam bridge. During the Tang Dynasty, many famous stone beam bridges appeared. According to "Tang Liudian", there are four famous stone beam bridges in the world: Tianjin Bridge, Yongji Bridge and Middle Bridge in Luoyang, Henan, and Xiong Bridge in Xi'an. The Qiao Bridge is a stone pillar pier and wooden beam bridge located on the Qiaoshui, 20 miles northeast of Xi'an. Since the construction of the bridge in the Han Dynasty, it has been destroyed and repaired for two thousand years. It took nine months for the thirteenth year of the Qing Dynasty (1833 AD) to build today's multi-span bridge. The bridge is nearly 400 meters long, with 67 holes. The net span of each hole is about six meters, and the bridge is about seven meters wide. The pier consists of six stone pillars. The top of the six stone pillars is covered with a stone beam, and they are integrated into one, forming the earliest light pier in the history of the bridge, which is called the stone row pier today. This ancient bridge, which has been used for thousands of years as a traffic throat, has been transformed into a modern highway bridge today.

To

Wan'an Bridge, Quanzhou, Fujian

After the Song Dynasty, people's ability to overcome nature increased, and in Quanzhou, Fujian, China's first large-stone beam bridge Wanan Bridge, Luoyang Bridge, was built. The bridge is 834 meters long and seven meters wide. There are islands in the middle of the bridge, seven holes in the south of the island and 41 holes in the north of the island. Each hole spans about 11 meters. The place where the bridge was built was right into the estuary, the current was turbulent, and there were many earthquakes and typhoons in the local area. The construction of the bridge was quite difficult. This is covered in the next section of this book. After the Luoyang Bridge was built, it became a sensation. It has the reputation of "the first bridge in the world", thus setting off a "bride of building bridges" in the local area. During this period, Fujian s newly-built stone beam and stone pier bridge reached new levels in terms of length, span, weight, construction speed, construction technology, bridge type, and bridge foundation, and occupied an important position in the history of Chinese and foreign bridge construction. The prominent ones can be represented by Anping Bridge in Jinjiang City, Fujian Province, and Hudu Bridge in Zhangzhou City. The Anping Bridge has a total length of 811 feet, more than five miles, and 362 holes. It is an ancient long bridge rarely seen in the world, and is known as "there is no such bridge in the world". The largest stone girder of the Hudu Bridge is 23.7 meters long, 1.7 meters wide, 1.9 meters high, and weighs 207 tons. It is the heaviest stone girder in the world.

With the development of social productive forces, the form of beam bridges is constantly changing. For example, in China's Jiangnan water villages, people often build such bridges into a figure-shaped or stepped structure with a large middle hole and a small side hole. The bridge heads on both sides are also built with steps with very unique steps to attract people to the bridge. There is also a fiber bridge parallel to the river beside the canal from Shaoxing to Hangzhou. Some ancient stone girder bridges have gates under the bridge or channels on the bridge, making one bridge more versatile. According to historical records, in the area where the border between Gansu and Xinjiang was called Duanguo in ancient times, there was a wooden bridge with outriggers. This kind of bridge adopts round wood or square wood stacked vertically and horizontally, and is picked out from the upper layer of the bank or pier to the center of the river valley, just like the layered bucket arch in the ancient building. Locals call this kind of bridge "flying bridge", which is easy to see in the woody areas in the south. Some bridges also have bridge houses or bridge porches, which have colorful paintings, Buddha statues, and bridge views like flowers, so they are called flower bridges. In the New Year, the Flower Bridge has become a place for people to entertain, catch up, and catch temple fairs. For example, the Guangxi Sanjiang Chengyang Bridge is a famous flower bridge that organically combines function and decoration. In addition, there are wooden braced bridges and beam bridges with outrigger wooden beams and braces.

The earliest recorded girder bridge in the history of our country is the Qiao Bridge, built in the Shang Dynasty (16th ~ 11th century BC). King Zhou Wu cut down, Ke Shangdu Chaoge (now Chaoge Town, Hebiqi County, Henan Province), Fajiu Bridge (Jiaoqiao Town, Jun County) to save the poor. Since the Qin Dynasty, Qin Khan has built stone pillars and wooden beam bridges in China.

In the Song Dynasty, numerous stone pier and stone beam bridges were built. For more than 200 years, in Quanzhou alone, there are 110 bridges seen in ancient books, including 10 famous bridges. For example, Anping Bridge has 362 holes and a bridge length of 5 miles (2223 meters), so it is also known as the Wuli Bridge (currently the bridge length is 2100 meters) and has maintained a bridge length record of more than 700 years. The bridge was built in Song Dynasty, eight years in Shaoxing (1138 AD), and completed in Shaoxing twenty-one years (AD 1151), which lasted 13 years.

Another example is Quanzhou Wan'an Bridge, commonly known as Luoyang Bridge, with a total of 47 holes, built at the mouth of the Luoyang River. The total length of the bridge is about 890 meters and the bridge is 3.7 meters wide. The bridge was built in five years of Song Huangyou (AD 1053) and completed in four years of Song Jiayou (AD 1059). Both bridges are national key cultural relic units.

The stone beam of Jiangdong Bridge in Zhangzhou, Fujian is the largest. The bridge was changed from a wooden beam bridge to a stone beam bridge in the first year of Song Jiaxi (AD 1237), with 15 holes and three stone beams per hole. There are currently 5 holes in the stone bridge. The largest stone beam is 23.7 meters long, 1.7 meters wide, 1.9 meters high, and weighs 2000 kN (kN) (200 tons). Such a huge stone beam, in ancient times without heavy lifting equipment, its mining, transportation, installation and other tasks were very difficult.

Regardless of the wooden beam or stone beam, in order to lengthen the bridge span, a multi-layer side-by-side beam is adopted, and the method of picking out from the bottom to the upper layer is adopted to support the simply supported beam in the middle. At that time, stone beams were called stacked; wooden beams were called flying bridges or grip bridges, which were outrigger beam bridges. Wooden outriggers were recorded in the 4th century. The stone bridge is astringent, not far from the eaves; the wooden bridge reaches 20 meters. Existing Yinping Bridge in Wenxian County, Gansu Province

Yinping Bridge, Wen County, Gansu

Kongmu outrigger bridge, the bridge spans over 60 meters, and a bridge house is built on the bridge.

The wooden beam bridge is generally built with a bridge house or bridge porch. Chengyang Yongji Bridge in Guangxi Sanjiang Dong Autonomous County is a 4-hole, 5-pier wooden outrigger bridge house with a total length of 644 meters. It was built in 1916. There are bridge pavilions on 5 piers and platforms. . The bridge pavilion plays the role of gravity balance, organically combining decoration and function.

Beam bridge characteristics and application occasions

1. Because the cantilever beam can reduce the height of the inner main beam, it has a lighter weight and saves material. Moreover, the height of the mid-span building is small, and the height of the beam at the bridge pier is large, so it is beneficial to the navigation clearance.

2. Because the internal force distribution is similar to a continuous beam bridge, the basic size and material usage of a cantilever beam bridge with a medium span are also similar to a continuous beam bridge. There is only one row of supports on the bridge pier, so the width of the pier can be reduced.

3. Especially in the plain area, most of them are soft ground, and the navigation span of the river is generally 40-50m. It is more economical and reasonable to use a cantilever beam bridge. Because the cantilever beam bridge is a statically indeterminate system, the internal force of the section will not change when the foundation settlement is uneven.

4. The cantilever end of a cantilever beam bridge is prone to deflection under constant and live loads. Especially for cantilever beam bridges that use high-strength prestressed steel wire as prestressed material, the prestressed steel wire has a large slack, which affects the main beam The decrease of the provided prestressing force will cause the cantilever end to fold down, and the driving comfort is poor.

5. Where the span of the middle hole is within 30m, a reinforced concrete cantilever bridge can be used. For 30 ~ 50m, a prestressed concrete cantilever bridge should be used; when 50 ~ 100mm, a single cantilever + hanging hole of the arch-beam combination system should be used . The middle span of 80m has been completed in Jiangsu's southern Jiangsu area. Using traditional arch bridge construction techniques, combined with cast-in-place tensioning on the shore and land, and finally using the swivel construction method to complete the bridge, regardless of the construction process and economic indicators Competitive. The result of practice is 20% ~ 25% less than that of similar span bridges. ^[5]