In the field of bridge engineering, steel truss has become a common structural form due to its high strength, large span and good mechanical properties. However, changes in ambient temperature can cause steel truss to produce thermal expansion and contraction effects. If this effect is not handled properly, it will pose a serious threat to the stability of the bridge structure and also profoundly affect the design of the bridge.
Steel truss is a complex structural system composed of many rods. When the temperature changes, the rods will deform due to thermal expansion and contraction. When the deformation is constrained, temperature stress will be generated inside the structure. For example, in a continuous steel truss bridge, the piers and supports will constrain the expansion and contraction of the steel truss. The resulting temperature stress will cause the rods to bear additional axial force, bending moment and shear force. If the temperature stress is too large and exceeds the bearing capacity of the rod, it may cause the rod to crack or even the entire structure to be destroyed. In some large steel truss bridges across rivers and seas, due to the long length of the bridge, the cumulative deformation and stress caused by temperature changes are more significant, and the impact on the internal force of the structure cannot be ignored.
When the temperature rises, the steel truss rods extend, and the entire structure produces an elongation displacement; when the temperature drops, the rods shorten and the structure produces a contraction displacement. If this displacement exceeds a certain range, it will affect the normal use function of the bridge, such as uneven bridge deck, affecting driving comfort and safety. For railway steel truss bridges, excessive displacement may also affect the smoothness of the track and increase the safety hazards of train operation. In addition, the displacement caused by temperature changes will also cause relative displacement between the steel truss and the piers and abutments. Under long-term repeated action, the bolts at the connection may loosen and the welds may crack, thereby affecting the stability of the structure.
The node connection of the steel truss is a key part to ensure the integrity and force transmission performance of the structure. The thermal expansion and contraction effect caused by temperature changes will cause the rods at the node to produce relative displacement, thereby exerting additional force on the node connection. For welded nodes, temperature stress may cause cracks in the welds; for bolted nodes, the expansion and contraction of the rods caused by temperature changes may cause the bolts to bear alternating loads, resulting in loosening of the bolts or even fatigue damage. In some steel truss bridges connected by high-strength bolts, if the influence of temperature changes is not fully considered, the reliability of the node connection will gradually decrease over time, threatening the safety of the bridge structure.
In order to cope with the thermal expansion and contraction effects caused by temperature changes, a series of optimization measures need to be taken in the design stage of steel truss bridges. In terms of structural system design, expansion joints should be reasonably set so that the steel truss has a certain expansion space when the temperature changes to release temperature stress. The spacing and structural form of the expansion joints need to be determined comprehensively based on factors such as the temperature change range and bridge length in the area where the bridge is located. At the same time, a temperature self-stress release system is adopted, such as setting movable hinge supports and sliding supports in steel trusses, to reduce the constraints of the structure on temperature deformation and reduce temperature stress.
In terms of material selection, steel with a smaller linear expansion coefficient is preferred to reduce the deformation of the rod caused by temperature changes. In addition, the structural details of the steel truss are optimized, such as strengthening the structural measures of the node connection to improve the fatigue resistance and bearing capacity of the node. For welding nodes, reasonable welding processes and weld forms are used to reduce welding residual stress; for bolt connection nodes, anti-loosening measures are adopted, such as using double nuts, spring washers, etc., to ensure the reliability of bolt connection.
With the development of science and technology, the introduction of temperature monitoring and early warning systems in the design of steel truss bridges has become an important trend. By installing temperature sensors at key parts of steel truss, the temperature changes of the structure are monitored in real time. Combined with the structural mechanics model, the internal forces and displacements of the structure caused by temperature changes are calculated. When the monitoring data exceeds the set threshold, the system automatically issues an early warning so that maintenance measures can be taken in time. This intelligent monitoring method provides a strong guarantee for the safe operation of bridge structures and provides actual data support for the optimization of design schemes.
In the construction process of steel truss bridges, choosing a suitable construction temperature is crucial to controlling temperature stress. For example, when assembling and welding steel trusses, try to choose a period with a relatively stable temperature to reduce the additional stress caused by temperature changes. During the operation and maintenance phase of the bridge, the working conditions of expansion joints, supports and other components are regularly checked, and debris in the expansion joints is promptly cleaned to ensure free expansion and contraction; node connection parts are inspected and maintained to prevent problems such as loose bolts and cracked welds. Effective temperature control during the construction and maintenance phases ensures the structural stability and service life of steel truss bridges in temperature-changing environments.
