Lateral trusses between I‐girders introducing torsional stiffness to a composite bridge in Guatemala

The ways of designing and building steel girder bridges with a composite concrete deck vary much between different parts of the world. A bridge system with twin steel I‐girders or a concept with multiple (more than two) girders can be used. The design and use of details and secondary systems also vary a lot. In order to give horizontal stabilization and distribute horizontal loads, bracing between the I‐girders bracings are often used. Although not so common, the bracing can also be used to distribute vertical loads between the main girders. To describe and to analyze the possible impact from using a lateral bracing, this paper describes the design of a curved bridge in Guatemala City and its challenges. The new Bridge over the Pinula River is designed as a steel‐concrete composite bridge with multiple steel girders with a concrete deck on top and has lateral bracing between the girders. The bridge is used as a case study to analyze the impact from a lateral bracing system on the vertical load distribution between the longitudinal girders. The bridge was designed with lateral bracing between the top flanges along the whole bridge and with bracing between the lower flanges near the supports. The case study shows that the distribution of eccentric vertical loads between the longitudinal girders can be improved by using lateral bracing between the lower flanges for multiple girders. In some cases, it may not be beneficial to use lateral bracings along the whole bridge length, like for example this bridge. In this case due to the governing design cases in the construction stages where these bracings influenced the torsional stiffness of the bridge in such way that an unfavorable distribution of the support reactions between the six girders at some supports was achieved.