Abstract: Taking a six-storey steel frame construction as the research object, parameters under study are the horizontal space of braces’ nodes and the layout of vertical braces. Based on the analysis of the structural period, layer displacement and angles of storey drift, research on the influence of layout of braces on structural dynamic properties of large space buildings is conducted. The results show that when column spacing is larger, braces-setting contributes to significantly improve the structure’s lateral stiffness and reduce the section size of columns, and that the section size of braces can be reduced by shortening the horizontal space of braces’ nodes. Braces should be set between the columns as full as possible. It is better to set the vertical braces positioned in the center instead of on the side between the columns. The lateral stiffness is higher when braces are set concentratedly than dispersedly. It’s more economical to set the inclined braces uniformly.
Abstract: The damping characteristic and dynamic responses of the concrete-filled square steel tubular (CFST) columns were numerically investigated in this paper. Finite element iteration method in the hysteretic damping system for CFST materials was presented, and an improved method considering viscous damping dynamic equilibrium equation with hysteretic damping model was also proposed. Based on the proposed methods, the loss factor and dynamic response of CFST columns subjected to the earthquake and harmonic loadings were effectively calculated. The results indicate that the stress-dependent damping method induces a larger dynamic response, and the loss factor of the CFST columns increases with the increase of the stress amplitude and lower steel ratio.
Abstract: The global earthquake disaster happened frequently in recent years, how to guide the construction correctly in seismic area becoming a problem to be solved, while the study on the tunnel geological advanced prediction system in seismic area is limited. This paper established an integrated prediction system which was combined with engineering geology analysis and geophysical method combined with the analysis of the characters and reasons of tunnel disaster in seismic area. And then, based on the forecast results, the interval of the groundwater correction factor K1, main strike-dip of structural surfaces correction factor K2, the initial stress state influence correction factor K3, which affected basic quality indicator of surrounding rock BQ were divided. At last, the dynamic division of tunnel surrounding rock classification was made by using of comprehensive evaluation method of surrounding rock classification. Construction feedback information showed that the forecast results were accurate and it played a good role to guide the tunnel construction.
Abstract: When vertical hybrid structures of steel reinforced concrete-steel (SRC-S) are used in multi-story and tall buildings, the connection between the two structural systems would probably dissatisfy the seismic request because of the abrupt change of stiffness. Setting up a stiffness-transition-layer is an efficient way to improve the seismic performance. In this paper, elastic and elastic-plastic analysis was conducted on a six-floor frame structure by Midas software. In the building, concrete encased shape steel was applied as the transition layer. By comparative analysis, we tried to find out how different transition layer positions could affect seismic performance in SRC-S vertical hybrid structures. Given the results, transition layer position has great influence on the story drift angle, story drift and the development of the plastic hinges. The suggestion on transition layer position was proposed to provide a reference for seismic design.
Abstract: A method based on Approximate Entropy (ApEn) Theory is proposed to assess the damaged condition of concrete beams from the vibration signals generated by means of excitation on beams. The presented method no longer concerns about identifying modal parameters of the structures but about estimating the regularity of the time series. Simply-supported concrete beams were monotonously damaged and followed with an investigation of the vibration signals generated from the excitation on these damaged beams. The ApEn method was successfully employed to the generated signals for an assessment of the damage status of concrete beams. In addition, comparative studies between traditional method (Wavelet Transform) and ApEn method show that the latter is capable of capturing the deterioration of these concrete beams with more sensitive characteristics. The ApEn method proposed is of great promise to be applied in real concrete structures.
Abstract: After the "5.12 wenchuan" earthquake, the fortification intensity of part of the affected areas has adjusted, most of the structures especially the Public buildings need to reinforcement after the fortification intensity was adjusted. In this paper, based on a sports teaching training center which is building when the earthquake happening, with the particularity of the fortification intensity increased, evaluated the seismic performance of the structure before and after fortification intensity increased, and dynamic analysis on the finite element model of different HADAS reinforcement schemes has been done, then evaluated the shock absorption effect under different reinforcement schemes. The results show that: 1) HADAS has important role to adjust the vertical stiffness, enhance the capability of energy consumption, and improve the damping performance of structure; 2) HADAS should decorate in the layer which has larger inter-story displacement angle, that is the neighboring story of stiffness changes greatly; 3) the number and arrangement mode of the HADAS has optimal solution and so on.
Abstract: Due to the massive volume of body and complex structure, the dynamic reliability analysis on arch dam under earthquake action draws more attention. In this paper calculated seismic dynamic action on arch dam by applying mode superposition response spectrum method. By taking the elastic modulus of the dam concrete and the rock foundation beneath the dam, and concrete tensile and compressive strength as random variables, adapting response surface method to establish limit state equation. The reliability index of each element in the dam was calculated via gradient optimization method, as a result to obtain the variation law of reliability index of dam body. The calculation of real case shows that the tensile index is comparatively low at some region of dam heel and abutment upstream, which requires the measure for aseismic measures, while the reliability index for tensile and compressive stress on other part of dam generally meets requirement.
Abstract: In order to study the influence of the crack-depth ratio on reinforced concrete fracture parameters and the resistance of the reinforcing bar to crack propagation in concrete, the fracture tests were carried on by using four groups three-point bending specimens with initial crack-depth ratios of 0.2, 0.3, 0.4 and 0.5 in this paper. An analytical model was presented to calculate fracture toughness of reinforced concrete by analyzing crack propagation process of the three-point bending beams. The formula of calculating effective crack length of reinforced concrete was established. The research results show that the double-K criterion can be used for describing crack propagation process of reinforced concrete by introducing fracture toughness, which is suitable for reinforced concrete. Initiation fracture toughness and unstable fracture toughness of reinforced concrete slowly increase with the increase of crack-depth ratio, which is different from the properties of ordinary concrete. The reinforced can improve the ductility of concrete obviously and inhibit the rate of crack propagation well.
Abstract: Existing deep reinforced concrete (RC) coupling beams with low shear span ratios and conventionally reinforced shear stirrups tend to fail in a brittle manner with limited ductility and deformability under reversed cyclic loading. Experimental and numerical studies have demonstrated the effectiveness of laterally restrained steel plate (LRSP) retrofitting method in improving the seismic performance of deep RC coupling beams. In this way, the deformability and energy dissipation of the retrofitted beams are greatly enhanced. Based on the experimental studies and numerical simulation of LRSP coupling beams, an original design procedure on the ultimate strength of LRSP coupling beams is proposed. The proposed design guidelines consist of seven parts, which are (1) estimation of shear capacity of RC component, (2) estimation of plate size, (3) design of bolt group, (4) estimation of axial force, (5) determination of buckling effect coefficient, (6) shear resistance design of the retrofitted beam, and (7) flexural resistance design of the retrofitted beam.
Abstract: The mechanical properties of non-dispersible underwater concrete short columns and the common concrete short columns under low cyclic reversed loading were carried out by experimentation in this paper. The results showed that, the seismic performance of non-dispersible underwater concrete short columns and the common concrete short columns are similar, so the seismic performance of non-dispersible underwater concrete short columns can be calculated by the seismic theoretical of the common concrete short columns.