Applied Mechanics and Materials Vols. 226-228

Abstract: The structure influencing coefficients reflect discount rate on horizontal seismic action of different structure categories. In general, the structure influence coefficients are related with the ductility level and overstrength of the structure. According to Code for seismic design of buildings (GB50011-2008), four models of three story-steel frames are designed for 4 types of site. Dynamic time-history analysis is carried out to study the models with records of seismic waves. The ductility level, the over-strength and Structural Influencing Coefficient are derived by the energy concept in the different sites condition. Structural Influencing Coefficient based on the energy concept is a new attempt. Method of the energy concept and design of structure will become the important development direction to improve the traditional seismic design.

Abstract: Based on the background of a subway construction project, deterioration characteristics of the existed subway tunnels under long-term train loads is studied by using the method of stiffness discount which could reflect fatigue damage of the structure. Firstly, dynamic response of the tunnel with initial defects caused by approaching construction under long-term train loads is analyzed according numerical simulation, and some results under different degrees of fatigue are obtained. Then, numerical results of acceleration responses at such different points as the upper vault, the side wall and the bottom of tunnels in two directions, are compared with each other while the train loads are applied at the left tunnel, especially under three different stiffness. Our investigation shows local structural damage in the position with initial cracks will be caused by a high cycle stress although there are fewer influences of stiffness changes on dynamic response of tunnels.

Abstract: The influence of vibration on surrounding structures is one of the most important factors considered during blasting demolition of high-rise buildings in metropolitan regions. In the controlled blasting demolition of a 22-story RC building in Kunming, several accelerograms on ground surface were observed. Based on analyses of vertical peak ground velocity which is normally used in blasting vibration evaluation, and horizontal spectral acceleration which is frequently used in earthquake engineering, the ground motion caused by building collapse was evaluated. The results indicated that the adoptive vibration decreasing measures had a good effect, and the slight damages of two nearby buildings could not be due to abnormal strong ground motion caused by collapse.

Abstract: SRC (Steel Reinforced Concrete) columns have a very broad application in the construction industry, and their cross-section combined forms are becoming more and more diverse. To solve the strength and stiffness problem of special-shaped SRC columns fast and accurately, the formulas of bending stress and bending deflection of special-shaped SRC columns were derived based on plane assumption from the bending experiments of SRC columns. For the problem with a eccentric force, the formula of normal stress from axial force was derived and added to the bending stress. Based on the formulas, the program is implemented to calculate the bending stress and bending deflection of special-shaped SRC columns. The example results showed the formulas are simple and reliable, and have certain engineering meanings and theoretical value.

Abstract: Liquefaction is one of the most important damages in pile foundation under earthquake. However, it is very difficult to analyze. Numerical simulation of pile-soil interaction considering saturated sand liquefaction under earthquake is conducted using OpenSees program. In this model, the soil is divided into soft clay soil and saturated sand, and the single pile is embedded in the soil. The results show that the pore water pressure rises and the soil liquefied as vibration time increases. With the nonlinear of the soil develop, the stiffness, bearing capacity and the acceleration response of the soil and the pile decrease, while the displacement response of the soil increases. Therefore, it is necessary to consider the soil liquefaction in the design and analysis in the engineering practice.

Abstract: This paper numerically investigates the tilt response of multi-storey buildings due to progressive collapse of the adjacent underground structure under internal blast loading. The software LS-DYNA is utilized to establish a three-dimensional coupled model composed of the underground structure, the soil around and the adjacent above-ground structure. In order to reduce the computational cost, an efficient computational method, Three-Stage Simulation Method (TSSM), is put forward. Three different methods, Alternative Path Load Method (APLM), Direct Simulation Method (DSM) and TSSM, are used to analyze the same model which illustrates the correctness of the model and the proposed method. By comparing tilt response of the above-ground structure of different types due to progressive collapse of underground structure under its internal blast loading, it is found that the tilt response of the above-ground structure of different types is related to the foundation of the structure. For example, compared with the frame structure with basement, the frame-shear wall structure with basement can prevent structure from great tilt response. However, the tilt response of the frame-shear wall structure with raft basis is larger than that of the frame.

Abstract: Stainless steel 304 and 316 (ss304 and ss316) are widely used in heat exchangers, and the precipitation characteristics of CaCO3 is the first step to research anti-fouling technology. CaCO3 scaling precipitated on coupons from 1.0mmol/l CaCO3 solution at 35°C. By weighing the coupons before and after static reaction experiments to get the mass of scaling and the morphology was taken by Scanning Electron Microscope (SEM). The results show that at the same condition there is more fouling on ss304 than ss316. Higher pH not only promotes square aragonite and calcite and square aragonite gradually recrystallize to calcite but also makes both homogeneous and heterogeneous nucleation rate increasing, and the former increases more, so the fouling mass is bigger at lower pH than higher pH; fouling grows at the place with higher surface energy first and then extend to surrounding place, and when the number increases and crystals grow big and connect each other to form fouling layer.

Abstract: The progressive collapse of a multi-story building and its protective effect with aluminum foam under an explosion in its basement are numerically investigated in this paper. The three-dimensional coupling model composed of a multi-story frame structure with a basement and the surround soil is modeled using ANSYS/LS-DYNA. The progressive collapse of the entire structure under explosive impact and the protective effect of the aluminum foam are simulated using the proposed three-stage simulation method (TSSM). The result shows that, the aluminum foam as a protective layer can reduce the impact effects very well, and then can prevent progressive collapse effectively. The same model is also simulated by direct simulation method (DSM) and alternative load path method (ALPM). By comparison with the two methods, the TSSM is illustrated practical, accurate and economic for the analysis of progressive collapse.

Abstract: Dynamic response of an underground structure with the protection of foamed aluminum under internal blast load, compared with that without any protection, has been investigated numerically in this paper. The three dimensional model of the two-storey and two-span underground structure covered with soil around was built with the explicit dynamic analytical software LS-DYNA. The three-stage simulation method （TSSM） is proposed. And the middle column of the structure is covered with foamed aluminum which provides a better protection for the column under the blast load. The solid-fluid interaction algorithm, the erosion algorithm and the stress initialization method are employed in the calculation. It is found that, under the protection of foamed aluminum the collapse resistance of the structure has been improved greatly compared with the structure without any protection.

Abstract: Two simply supported beams with a shear span to depth ratio of 2.2 were tested, one with straight prestresssing tendons and the other without for reference. The shear behavior and the prestressing effect are focused on. The test results showed that the prestressed concrete (PC) beam has a significant arch effect, and the prestressing could greatly increase both the cracking load and the shear strength. Besides, the Modified Strut-and-Tie Model (MSTM) and the sectional design method from China Code (GB10) and ACI318-08 have also been adopted for predictions. The comparisons indicates that the MSTM can not only well predict the shear strengths of PC beams with a small shear span to depth ratio, but also well account for the prestressing effect, while the sectional design method seems so conservative due to its not properly considering the shear mechanism of such beams. It can be concluded that the MSTM is capable of predicting the shear strength of PC beams with significant arch effect and thus can be employed in practical designs.