# Seismic Analysis of Steel Solid Web Girder-RC Tubular Column Hybrid Structure
## 1 Introduction  
Steel-concrete hybrid structural systems are obtained through the combination of structural components made of steel, reinforced concrete (RC), and composite steel-concrete. They are more efficient and economical compared to either traditional steel or RC structures, since they can make full use of the advantages of different materials [1; 2; 3; 4]. A great deal of research on steel-concrete hybrid structures has been carried out in the past, and many high-rise buildings have applied steel-concrete hybrid structural systems [5; 6; 7]. Especially for industrial buildings, a steel-concrete hybrid structure is a good structural system to realize flexible structural layouts to meet special industrial and load demands [8; 9; 10]. Attention in this study is focused on a peculiar steel-concrete hybrid structure typically applied as the supporting structural system to house air-cooled condensers (ACCs) in thermal power plants (TPPs).  
Nowadays, the most popular supporting structural system in TPPs is the steel truss-RC tubular column hybrid structure, which consists of A-shaped steel frames, steel space-truss platform and RC tubular columns [11; 12]. However, past research results showed that this kind of structural system issuitable for a medium capacity of TPPs of no greater than 600 MW because of its lower lateral and vertical stiffness [13]. To satisfy the design requirements with the increase of unit capacity of TPPs, several researchers proposed a novel supporting structural system named the steel braced truss-RC tubular column hybrid structure, in which diagonal steel braces were used to connect the steel truss and RC tubular columns to upgrade the structural safety performance [14,15]. However, since there are too many steel elements and connections in this kind of hybrid structure, the constructions are rather complex, and the cost is very high. To solve this problem, some researchers suggested to replace the steel truss by using the steel solid web girder in two orthogonal directions, developing a novel supporting structural system referred to as steel solid web girder-RC tubular column hybrid structure, which has been applied in practice. Figure 1 shows the schematic diagram and a typical photo for this kind of hybrid structure. Similar with the steel braced truss-RC tubular column hybrid structure, steel diagonal braces were used to connect the RC tubular columns and the solid web girder. In addition, steel braces were also set below the solid web girder to improve the overall stiffness of the platform. The statistical analysis showed that the amount of steel used in the steel solid web girder-RC tubular column structure could decrease about 30% compared with the steel braced truss-RC tubular column structure [16]. However, the seismic performance of the steel solid web girder-RC tubular column hybrid structure has not been verified yet.  
In this study, the seismic analysis of a steel solid web girder-RC tubular column hybrid structure was conducted. First, numerical modeling approaches were validated by a range of pseudo-dynamic test results. Then, the numerical model of steel solid web girder-RC tubular column  
Figure 1: Solid web girder-RC tubular column hybrid structure: (**a**) Schematic diagram; (**b**) A typical photo of practical engineering.  
hybrid structure was developed to carry out the elasto-plastic time-history analysis. The dynamic characteristics, time-history curves of base shear force and roof lateral displacement, lateral deformation pattern, maximum drift ratios, lateral stiffness deterioration, and damage evolution characteristics were analyzed.