2021 Vol. 36, No. 8

Evaluation of Seismic Performance for Outrigger System and Ladder System in High Rise Buildings
Yahia Halabi, Wael Alhaddad, Hu Xu, Zhixiang Yu
2021, 36(8): 1-19. doi: 10.13206/j.gjgSE20111001
Excellent seismic performance of high-rise building is a continuous destination in structural engineering, that highly relies on the lateral load resisting system. As one of the most common lateral load resisting systems, the outrigger system is widely applied to skyscrapers. However, its mechanical properties are affected by the truss location, the topological form as well as construction process, in addition, the irregular vertical stiffness of the entire building occurs. Therefore, the actual seismic behavior and optimization methods are worthy paying attention to. The ladder system is a novel lateral load resisting system, in which the horizontal beams are set to connect the mega columns at each floor, resulting in a more uniform vertical stiffness compared with the outrigger system.
In order to compare the seismic performance between the above two systems, the numerical models of 80-story building were established by means of the finite element program ETABS, and the performance-based seismic design method is adopted to carry out calculation and analysis. For the outrigger system, four levels of steel outrigger trusses were set along the height, and the specific locations that floor 17-18, floor 32-33, floor 46-47, and floor 62-63, respectively, were determined by considering the multiple factors including structural weight, base moment, base shear, inter-story drift, and core moment. In addition, the optimum topology of the outrigger truss was selected out of four different trusses' topologies with the same steel consumption according to the favorable natural period and the global response of the structure, such as base shear, bending moment and inter-story drift under the action of frequent and moderate earthquakes. Subsequently, the ladder system was generated based on the principle of the equivalent lateral stiffness with the outrigger model, and the cross section as well as the design parameters were presented.
Nonlinear dynamic time history analysis was carried out to compare the global and components' performance between the outrigger, ladder, and stand-alone core systems under the FEMA356 guidelines requirements, where 7 sets of natural ground motions and 2 sets of artificial ground motions for different intensities were selected as a seismic input. The results showed that:1) comparing with the stand-alone core system, the inter-story drift under the frequent earthquake level was reduced by 60% and 47% in outrigger and ladder systems, respectively. While the modification factors of both systems equal to 1, denoting that outrigger system is more efficient in the elastic stage. However, under the rare earthquake, the inter-story drift reduction was 56% and 70% for outrigger and ladder systems, respectively. While the modification factors of two systems equal to 3 and 6, indicating that the ladder system has better ductility and energy dissipating performance in the elastoplastic stage. Besides, the top displacement response of both systems reflect the same structural deformation feature. This indicates that the outrigger system is more effective in the elastic stage, while the ladder system is more ductile in the elastoplastic stage dissipating more input energy. 2) The same trend was for the internal forces, where the outrigger system reduced the core bending moment under the frequent earthquake level, while the ladder system showed a superiority under the moderate and rare earthquake evaluation. 3)In terms of the damage state evaluation, all the structural components in both outrigger and ladder systems were under Immediate Occupancy (IO) performance level for the frequent earthquake; while for the rare earthquake, most of the coupling beams reached the Collapse Prevention (CP) performance level in the ladder system, while only some of them reached the Life Safety (LS) and CP performance levels in the outrigger system. At the same time, the damage state of the shear walls was CP in both systems under the rare earthquake, and the damage state grew severer from lower to higher floors in the ladder system, however, the global plastic damage distribution has similarity between two systems. It can be concluded that the principle of the equivalent stiffness is more adequate under the frequent earthquake evaluation than the high earthquake intensity, where the calculation errors on energy dissipating and damage distribution would occur.
Experimental Study on Force Transmission of Squeeze Bolt in the Anti-Pull Support of Nuclear Containment
Xiangyu Zhang, Shasha Wang, Jinghai Gong, Te Tang, Jian Liu, Yuhang Zhou
2021, 36(8): 20-27. doi: 10.13206/j.gjgS20111001
The construction of AP/CAP series third-generation advanced nuclear power plants in China adopts an open-top construction method to facilitate equipment hoisting and ensure the continuity of equipment and module installation and construction in severe weather. The temporary opening and closing of the roof guarantee the smooth progress of the open roof construction. During the entire construction process of the nuclear power plant, three climbs are required. To be reusable in the same site, the temporary roof must be removable. At the same time, the top cover may encounter a 17-level typhoon, and the huge uplift force generated by the typhoon must be resisted by the uplift support of the top cover and the containment. Extrusion bolts are the key force transmission members in the anti-pull support. The anti-pull support is screwed into the extruded bolt supported by the vertical steel plate, so that the force transmission member and the containment are squeezed, thereby generating static friction to provide pull resistance. The extruded bolt in the antipull support is similar to the traditional clamping bolt. The bolt force is related to the relative roughness of each contact surface, bolt diameter, and bolt structure, but there is no relevant theory to determine the relationship between the tightening torque and the squeezing force of the bolt in the process of force transmission.
Given the above problems, this paper researched the force transmission of squeeze bolts. First, according to the different roughness of different force transmission members and contact surfaces, the friction block contact test, sleeve-friction block contact test, and flathead bolt contact test were designed to verify the necessity of setting friction block and the sleeve, and the improved method of spherical end bolt was proposed. Then, by adopting fixed torque electric wrench for staged loading, a method of directly establishing the relationship between electric wrench gear and bolt pressing force was obtained. Finally, based on the two sets of test results of the friction block and the sleeve being completely restrained and the spherical end bolts in direct contact with the containment, a method to improve the bolt force transmission was further proposed, and the dynamic friction coefficient between the friction block and the containment was obtained indirectly.
The following conclusions could be drawn. 1) The arrangement of friction block and sleeve minimized the damage of the anti-pull bearing to the containment during installation and use. When designing the bolt force transmission member, the spherical end bolt needed to be designed as the ellipsoid which was in approximate point contact with the socket groove and did not need to consider the influence of the thickness of the threaded hole on the force transmission of the bolt. 2) The directly established relationship between the gear position of the electric torque wrench and the extrusion force was useful for the engineering application of the electric torque wrench. 3) The obtained dynamic friction coefficient between the friction block and the simulated containment could provide a reference for the determination of the anti-pull resistance of the anti-pull bearing.
Overall Stability Capacity Analysis of Long-Span Single-Layer Special-Shaped Shell
Zhigang Ma, Guanghai Cui, Jing Wang, Xiaofeng Jie, Jing Li, Zao Jiang
2021, 36(8): 28-34. doi: 10.13206/j.gjgS20060901
As a cultural relic protection facility, the first site (Peking Man Cave) protection shield at Zhoukoudian Site is built to protect the main archaeological site from further weathering. The shield over the Peking Man Cave simulates the shape of the surrounding mountains and presents itself as irregular spatial surface. On the main long-span single-layer steel structure, double-layers blades are set. Sprawling herbs are planted in the grooves on the upper blades, and the lower blades are made by GFRP (glass fiber reinforced plastics) to model the rock texture. The structure will blend into the surrounding natural scenery from both inside and outside view angles when the plants thrive, and the design concepts for harmony and reconstruction of remote antiquity are realized.
In order to minimize the disturbance to the site and the surrounding environment, the main structure adopts a long-span single-layer special-shaped steel shell structure to control its volume. Due to the thinness, the single-layer grid structure provides more convenience for the double-layers blades installation. The global projection distance of the shield is 79 m in its longitudinal direction and 55 m in the transverse direction. The maximum oblique span is 83 m and the foundation height difference is 33 m. The shield is fixed by the hinge supports at the top and foot of the mountain. The safety of single-layer grid structure is often controlled by stability, which can be influenced by structural defects and boundary conditions. Three-dimensional and non-linear finite element methods are used to analyze and estimate the overall stability of the long-span single-layer special-shaped steel shell.
The stability ultimate capacity of the structure is analyzed by ANSYS software, and the influence factors of the stability ultimate capacity including the degree and distribution of overall structure defects as well as the stiffness of hinge support are investigated. According to the complete load-displacement curve, the stability ultimate capacity is confirmed. Analysis shows that the degree and distribution of overall structure defects have no obvious effect on the overall stability ultimate capacity as the shield is a complex spatial structure not an ideal shell, therefore, only the initial defect is taken into consideration for convenience of calculation. When initial defect of 1/300 of the oblique span is applied to the structure, and follow the first buckling modal shape distribution, the overall stability safety factor of the special-shaped shell is 3. 58, and the performance of the structure meets the requirements of Technical Code for Space Grid Structures (JGJ 7-2010). Analysis suggests hinge supports considering the significant effect of the boundary conditions on the stability ultimate capacity. The foundation anti-push resistance should be paid due attention to in design by the research.
The dynamic stability performance of the shield is analyzed by ANSYS software. Result shows that the special-shaped shell has satisfactory dynamic stability, and the damage seismic amplitude to cause dynamic instability can reach 0. 8g. The elastic buckling load of typical member of the special-shaped shell is obtained by applying unit force and eigenvalue analysis. The out-of-plane calculated length coefficient of members is determined as 1. 6 by inverse calculation of Euler formula, which meet the structural design requirements well and can be adopted for further reference.
Construction Technology
Research on Installation Technology of Multi-Layer Long-Span Steel Truss
Shuangxi Zhou, Tong Xu, Xiucheng Dai, Zu Wang, Zijian Zhang, Chaojing Xu, Weiquan Wang
2021, 36(8): 35-41. doi: 10.13206/j.gjgS20080501
The system of long-span steel truss is widely used in steel structure applications,it is commonly used as a single-story long-span steel truss system, and its installation method is relatively mature. However, there are few installation projects of multi-layer long-span steel truss structure system, and its installation technology needs further study.
The ground structure of the third-generation command center project in Shenzhen is a six-story continuous long-span steel truss system with a building height of 56 meters. Each floor is composed of six long-span steel trusses and steel beams, and the floor height is between 6. 5 meters and 12 meters. The project is located in a densely built urban area, and its storage yard and roads are very restricted. Through the comparison and selection of its installation methods, the construction methods of overall lifting and sliding installation were rejected, and the steel truss was installed at the corresponding position by a single-point support system with fast construction, safe and economical. By optimizing its structural form, the connection method and the top node, realizing the effect of quick installation and removal. The truss is arched during factory production, and the arching degree of the middle position is 60 mm during on-site installation. On the horizontal plane, the truss is installed in sections from south to north. On the elevation, a two-story steel truss is used as an installation unit. After the unit and the structure on both sides form a double-layer frame system, the lower truss support is unloaded and transported, and the floor is poured. After the floor is poured, the third floor of the truss structure is installed upwards, and the support system is turned up in this order for truss installation. Use MIDAS, which is a finite element analysis software, to simulate and check the force and structural deformation of the support system during the installation process in advance. Set deformation monitoring points at the middle and end of each truss, monitor and record it during the construction process.
The results of data comparison show that the simulated value is basically the same as the measured value; The successful application of this support system in the third-generation command center project in Shenzhen fully proves that this support system is fast, safe and economical in construction. The installation of the truss adopts a two-story steel truss as an installation unit. After the unit and the two sides of the structure form a double-layer frame system, the lower truss support is unloaded and transported. This method can effectively control the deviation during the construction of the structure.
Processing and Manufacturing
Fabrication and Installation Technology of Steel Truss Arch Bridge
Mingang Tan, Junping Li, Ping Che
2021, 36(8): 42-49. doi: 10.13206/j.gjgS21030101
Since the 1990 s, China's steel production has more than ten years in a row in the world, and the types of steel products, the quality has the very big enhancement, has reached the world advanced level in, the steel bridge in such aspects as design, manufacture, construction research and technology is increasingly mature, and steel truss arch bridge as a classic of bridge structure, with its stiffness of truss arch and downy derrick structure combination, form a sofe landscape architecture[3], has been widely used in bridge construction in our country. Because the horizontal thrust of steel truss arch bridge is large and the structure form is complex, it is necessary to integrate its structural characteristics, construction environment, equipment and other factors, and make a practical construction scheme on the premise of ensuring the construction quality and safety to achieve the purpose of cost reduction and efficiency increase.
Taiyuan Jinyang Bridge is a 204 m span steel truss arch bridge. The arch ribs are truss structure composed of upper chord, lower chord and X-shaped girder. The arch axis vector height of the upper arch rib is 48. 5 m, and the arch axis vector height of the lower arch rib is 42. 2 m. The main beam is connected with the tie beam and the arch ribs by welding. Through the analysis of the difficulties in rod making and site installation, the welding quality and welding deformation control measures of the tie beam and arch rib are formulated. The construction scheme is compared and selected and the key technologies such as steel beam bulk, arch rib pre-assembly and truss plate making are formulated. Combined with the structural characteristics and construction environment, some protective measures for aerial work are formulated.
The practice shows that the welding quality of the tie beam and arch rib is good, and the welding deformation meets the design and standard requirements. The steel girder adopts bulk packing scheme to increase the field working surface, improve the installation progress, and avoid the adverse effects of the increase of butt welding seam, the reversal difficulty and the long cycle caused by the general assembly. The implementation of the on-site pre-assembly and truss fabrication scheme ensures the quality of the truss fabrication, reduces the labor intensity and improves the installation precision of the truss. The protective measures for high altitude operation are practical and easy to operate, and good protective effect has been achieved.
Hot Spot Analysis of Steel Structures
2021, 36(8): 50-54.