Why are bearings installed in bridge structures?

Thermal expansion and contraction is a common phenomenon in nature; that is, objects expand when heated and contract when cooled.

Most elementary school children are familiar with this phenomenon.

                                                                                           Thermal expansion and contraction of air

In the engineering industry, the phenomenon of thermal expansion and contraction also exists.

During the process of thermal expansion and contraction, not only does an object change shape, but it also often causes changes in internal stress.

When an object expands or contracts due to temperature changes, the internal stress generated if the deformation is constrained externally or by internal unevenness is called temperature stress.

Ideally, the change in length of a linearly expanding object is directly proportional to its length.

ΔL = α∗L0\Delta L = \alpha\ast L_{0}\Delta L = \alpha\ast L_{0} ∗ΔT\ast \Delta T\ast \Delta T Where: ΔL\Delta L \Delta L —— Length change α\alpha \alpha —— Coefficient of linear expansion of the material (unit: 1/°C) L0L_{0}L_{0} —— Initial length ΔT\Delta T \Delta T —— Temperature change When an object reaches a sufficient length, the resulting deformation will not be negligible. For example, the arching and cracking of indoor floor tiles under hot temperatures.

                                                                                                Tile arching and cracking

In building construction, beams and slabs typically span only a few meters, resulting in relatively limited deformation.

However, roads and bridges are tens or even hundreds of times longer and longer than building beams and slabs. Furthermore, road surfaces and bridge decks are often directly exposed to the natural environment. High summer temperatures and harsh winter temperatures cause drastic temperature changes in bridges, leading to significant thermal stress and potentially more severe damage.

                                                                                               The road surface is arched (doesn't it look like arched tiles?).

A road surface suddenly cracked while a vehicle was in motion. This scene unfolded on August 13th on a road in Tongxiang City, Jiaxing, Zhejiang Province. On the 16th, relevant departments of the Tongxiang Municipal Construction Bureau told reporters from Jimu News that the road had cracked due to several days of continuous high temperatures, and repairs were currently underway in sections.

According to surveillance video posted by local netizens, two lanes of a road suddenly collapsed simultaneously, arching upwards and spraying dust. When traffic police arrived at the scene, another lane on the opposite side also suddenly cracked, with debris flying out, and several vehicles behind immediately stopped. Some netizens reported that several roads in Tongxiang City had experienced similar cracking recently.

                                                                                                                            Bridge deck arch

On July 23, Nan'an welcomed the Great Heat solar term. At 3:27:20 PM that day, the Dongmei Bridge in Renke Village, Hongmei Town, suddenly burst and bulged, with several shockwaves carrying sand and dust erupting from both sides of the bridge. Videos of the incident have circulated widely, drawing public attention. Reporters observed two large sections of concrete road slabs at the point of breakage, located on one side of the Dongmei Bridge.

The bulging concrete slabs were level with the guardrail, and the height difference between the bulging road surface and the normal bridge surface was approximately 50 centimeters. The adjacent guardrail was broken. Officials from Hongmei Town stated that preliminary investigations indicated the cause was the expansion joints of the concrete slabs expanding and contracting due to the high temperature. Currently, the town has reported the incident to the transportation department and invited experts to inspect and assess it. If the bridge piers are unaffected, further reinforcement and reconstruction of the concrete road surface will be carried out. If it becomes a dangerous bridge, other arrangements will be made.

To prevent bridge deck arching and breakage due to temperature changes, large bridges are typically equipped with expansion joints, which separate the beams at the expansion joints to allow the beams to contract and expand freely.

                                                                                                                              Bridge expansion joints

So here's the question: since the bridge beam can freely contract and expand, how are the piers and the beam connected? Does the beam's expansion and contraction cause the piers to tilt as well? ^ ^

Yes, you can use bridge bearings…

                                                                                                                                   Bridge bearings

Bridge bearings separate the bridge beam from the piers. Besides their load-bearing function, some bearings also allow for a certain degree of displacement and rotation of the bridge beam.

With the development of bridge technology in China, the forms and functions of bridge bearings have become increasingly diversified, with load-bearing capacities reaching tens of thousands of tons.

                                                                       Installation of bearings for the Hengtai River Bridge in Wanzhou, Chongqing

Bridge bearings are crucial components of bridges, serving as the connection points between the superstructure and substructure. The Hengtai River Bridge uses the largest hyperboloid seismic isolation bearings in China, with a vertical bearing capacity of 18,500 tons and a self-weight exceeding 100 tons.

"Chongqing is located in an area with a seismic intensity of 6 degrees, requiring earthquake resistance. Furthermore, the bridge uses a combined beam-arch structure with a lower deck, resulting in not only its heavy self-weight but also a 36-meter-wide lane width, making it a wide municipal bridge. Therefore, large-scale, ultra-large bearings were necessary," explained Ma Cunji, the technical head of the Hengtai River Bridge project at CCCC Fourth Harbor Engineering Co., Ltd. To overcome the difficulties of selecting and transporting the heavy bearings to the bridge, the Hengtai River Bridge adopted a split-installation process, separating the bearings into upper, middle, and lower plates for separate hoisting. The maximum lifting weight in a single operation was 47 tons.

So, are there bridges with a "rigid beam-column connection" as the questioner mentioned?

Of course, and there are many such bridges, such as continuous rigid frame bridges.

                                                            The Wudao Expressway Guanyinmiao Wujiang Grand Bridge was successfully closed.

The Guanyinmiao Wujiang Grand Bridge, invested by China Railway Construction Chongqing Investment Group, surveyed and designed by the First Railway Survey and Design Institute, and constructed by China Railway 21st Bureau Group, is located in Wulong District, spanning the Wujiang River waterway and National Highway G319.

"This is the largest span highway bridge of its kind in China," said Wan Pengzhou, the on-site manager from China Railway 21st Bureau Group. The bridge is 944 meters long, with a main span of 242 meters, main piers reaching a height of 115 meters, and a maximum navigable water level difference of 260 meters between the bridge deck and the river surface.