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The occurred damages during the past significant earthquakes have proved that vertical seismic excitation has tremendous effect on bridges. Three-component earthquake excitations are preferred to resemble the earthquakes. In this article, a cable-stayed arch bridge, a new type of bridge with the hybrid system of half-through arch and stay-cables, was analyzed under a set of different earthquake excitations (more than 21 ground motion records). Both vertical and horizontal components of the ground motions were considered to act simultaneously at the bridge supports. By using different three-component earthquake excitations, the dynamic responses of the bridge, including the displacements and accelerations of the main parts of the bridge, were obtained. The effects of various parameters such as soil type, epicentral distance, spatial variation of the ground motions, and dimensional variation of the structure were investigated. The results of the numerical study indicate that the cable-stayed arch bridge subjected to both horizontal and vertical components of earthquakes are more vulnerable than those subjected to horizontal ground motion only.

Vertical or inclined cables which are placed in bridges as a hanger system affect the dynamic performance of bridges. Inclined hangers can be used instead of vertical hangers to improve the stability of the bridge aerodynamically. However, inclined hangers are susceptible to fatigue more than vertical ones. Considerable signs of distress or slackness might be shown by some inclined hangers because of their location on the bridge. In this study, a cable-stayed arch bridge with vertical and inclined hangers has been compared to investigate the effect of hangers on the dynamic performance of the bridge. To reduce the internal cable forces and the probability of fatigue or force fluctuation in hangers, additional horizontal cables are applied on inclined hangers that transfer the tensile load from overstressed hangers to adjacent ones with lower forces. By modification, the results demonstrate the higher stiffness and human comfort level for the bridge that improve the dynamic behavior and control the responses of the bridge.

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Inclined hangers behave better than vertical ones under lateral loads (i.e., wind or earthquake) despite they are prone to fatigue phenomenon. In some instances, the slackness problem is seen in some inclined hangers, while others may become overstressed. By considering the modified hanger system, the disadvantages of vertical and inclined systems are resolved, while keeping their advantages. The objective of this study is to propose formulations for the optimum application of novel arrangement of hangers in a cable-arch bridge to suppress problems such as overstressing, force fluctuation, and decreasing the probability of fatigue phenomenon in hangers. To define optimum parameters, the modified hanger system was analyzed and compared with vertical and inclined ones considering nonlinear static analysis under dead load as an initial state plus seismic excitation and dynamic impact load of vehicles. Results indicate that the modified hanger system is improved remarkably in comparison with the inclined and vertical hanger systems.

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To investigate the optimum location of the outrigger system, a metaheuristic-based size and topology optimization of the outrigger-braced tall buildings is carried out by various three-dimensional structural frames with different shapes of belt trusses. By considering the elastic behavior, the whole elements of the structural models such as beams, columns, core, and trusses are optimized simultaneously in conjunction with the location of the outrigger. Furthermore, to reach more optimality, several novel types of belt truss are proposed having inclined and inverse-inclined belt trusses with better structural and architectural features and optimum performance in comparison with the horizontal one. Different models with 25 to 40 stories having various span numbers are optimized using the genetic algorithm, and the results are compared with each other. In the modeling process, the exact wind load distribution is applied to the structure based on the ASCE7-16 rather than the uniform or triangular ones. According to the results, the optimum cross-sectional size and outrigger locations of different models are obtained, and it is indicated that the proposed novel belt trusses are optimal solution for the problem. K E Y W O R D S outrigger-braced building, size and topology optimization, inclined belt truss, genetic algorithm 1 | INTRODUCTION Tall buildings' development has been an important issue from recent centuries. The risk of vertical and horizontal load forces also increases by increasing the building height. Over certain height, an auxiliary system is needed for the moment-resisting frames with the braced core in order to become efficient to provide stiffness against seismic and wind loads. To achieve the considered strength and stiffness in the building, the lateral displacement should be controlled in the analysis and design of a tall building. One of the auxiliary systems which leads tall buildings to have sufficient stiffness is the outrigger system. Tall buildings with outriggers and belt trusses are a common solution for tall MRFs as they are easy to build and cheap in comparison with the other structural systems. Outriggers interact with peripheral columns through stiff arms. Under large lateral load, the core's rotation at the level of outriggers causes a tension-compression couple in the outer columns which reduces the core deflection utilizing the belt truss that distributes the force to whole peripheral columns. Optimization of tall buildings as a large-scale structure is essential due to a large amount of materials used in their construction. Reaching the optimum weight lowers the consumption of resources and saves a considerable amount of money. To achieve the optimal design, using metaheuristic algorithms in case of tall structures will be an arduous effort because of the high computational costs due to the massive modeling process. One of the crucial parameters that should be considered in the preliminary design steps is the optimum location of the outriggers. For the