Advanced Materials Research Vols. 163-167

Abstract: According to the contrast test of LC30, LC40 lightweight aggregate concrete and C30, C40 common concrete , the text researched the mechanical property of lightweight aggregate concrete and ordinary concrete in the same strength grade and obtained the regularity of stress-strain curve of lightweight aggregate concrete in different strength grade. Then we contrasted the experimental results and planning model, analysed the difference, and suggested that the standards should improve the descent stage of the stress-strain curve of lightweight aggregate concrete combined with correlative experiments data, and give the equation of the descent stage of stress-strain curves. Concrete material in axial compression is the basic physical mechanical performance of concrete material, and is the main basis for researching bearing capacity and deformation of concrete construction. The stress-strain relationship is all-around macroscopic reaction of basal compressive property . There have been many experiments work about the stress-strain relationship of lightweight aggregate concrete at home and abroad , and found the peak strain of lightweight aggregate concrete is higher than that of ordinary concrete in the context of same peak stress .In this paper, on the basis of experimental investigations of lightweight aggregate concrete , aim at the stress-strain relationship ,we have take comparison experiment about LC30,LC40 lightweight aggregate concrete and C30,C40 ordinary concrete , and sort out stress-strain curve under the condition of the shaft center being compressed, so get the average tress-strain curve of LC30,LC40 lightweight aggregate concrete , and analyse the curve.

Abstract: At present, China lacks theoretical guiding and research on the concrete floor cracks control of residential projects, and there is no advanced experience of other countries for reference on some aspects. The concrete slab cracks of residential projects has become the focus of public attention, the hot spot of complaints and the difficult point of government business. To avoid the cracks has become a big problem and an important content in improving the residential projects’ quality, which demands prompt solution. This paper analyzes the causes of cracks from construction point, and puts forward some proposals from four aspects including formwork engineering, reinforced bar engineering, concrete engineering and aspect of construction management. This paper advances some immediate countermeasures, makes some moderate extensions on the strategic development of architectural technology and designs the solution orientation of the long-term countermeasures. These concrete solutions strive to be conveniently carried out, meanwhile give consideration to the economic legitimacy.

Abstract: With the development of construction industry, casting reinforced concrete floor has replaced pre-cast concrete hollow block floor with pre-stress. A large number of irregular cracks appear on the floor, which has become the biggest problem related to the residential projects’ quality. This paper analyses the causes of cracks and the major factors of the pre-mix concrete components and relevant material performances. Combined with current concrete technology, supply of raw material and production, and construction of concrete realities, controlling cracks can be begun to consider from two aspects, namely increasing the concrete strength and decreasing the concrete shrinkage. This paper puts forward the following measures to control cracks: 1. strict control of the water for concrete; 2.strict control of concrete slumps; 3. improving the quality of aggregate (such as sands or stones) and increasing the number of coarse aggregate; 4. Reasonable choice for additive; 5.controlling the amount of adulterant in concrete.

Abstract: Aimed to solve the problem that the mass concrete structures are apt to crack in underground engineering, this paper makes some research from the view of crack resistance performance of polypropylene fiber concretes. Since polypropylene fiber achieves waterproof through realizing of crack resistant, blending polypropylene fibers into concretes can reduce early contraction deformation of concretes, hinder emergence of plastic shrinkage cracking and improve impermeability of concretes, and its construction technology is simple. In practical application of this in anti-cracking and anti- seepage concrete structures in the International Terminal project of Hangzhou Xiaoshan International Airport, we find that mix of polypropylene fibers with concretes clearly improves anti-cracking and anti-seepage performance of concrete structures and meets design requirements of basements through measuring temperature and observing cracking condition of the mass concrete structures of basements on site. The project can provide experience for reference to similar projects.

Abstract: As a typical structural member, the dynamic behavior of RC shear walls under seismic dynamic loads and/or strong winds is a critical topic. In recent years, with the development of test facilities and numeric techniques, efforts have been made to study the dynamic behavior of RC shear walls under dynamic loadings experimentally and numerically. But available test results on the dynamic behavior of RC shear walls are limited because of the limitation of the large-scale test facilities for dynamic tests. In this paper, test on four RC shear walls under rapid loads are conducted and a finite element model of RC shear walls through introducing the strain rate effect to the concrete damaged plasticity model in ABAQUS is established to simulate the dynamic behavior of the four specimens tested. Through comparing the simulation result with the test result, it is clear that the developed dynamic damage plastic constitutive model of concrete can be employed to simulate the nonlinear behavior of RC walls with acceptable accuracy under dynamic load.

Abstract: Early cracks of box girder are widespread during the construction stage of PC box girder bridges. The cracking resistance of a prestressed concrete continuous beam bridge was conducted from the point of construction technique. Experimental study on hydration heat and mechanical properties of box girder concrete at early age were carried out. The results shown that the casting temperature of the concrete, the peak temperature and the maximum temperature difference between inside and outside of the hydration heat were very low, which were 15.7°C, 8°C and 10.2°C, respectively. The strength development of the concrete was stable, and the mixture ratio was optimal. The concrete appearance quality was fairly good without visible cracks in the construction stage. The study reveals that the crack of girder bridges during the construction stage can be avoided by taking effective measures in the construction.

Abstract: The free vibration of the eigenfrequencies and models of a rectangular p1ate with simply supported comp1eted clamped supported were calculated by finite element method using the quadrilateral heterosis element. Firstly, the basic Governing equations of Reissner-Mindlin plate for elastodynamics was introduced, And then the finite element model of the plate vibration was established, nine nodes heterosis element was adopted, the stiffness matrix and mass matrix were obtained. Selective-reduced integration scheme was carried out to eliminatethe curvature thickness and the transverse shear locking phenomena in the plate bending. Numerical experiments of plate free vibration using heterosis element with quadrilateral linear shape functions for the displacements was studied, eight models ware obtained which were closely to the closed solutions, the results show that the method successfully yields a stabilized element.

Abstract: Investigations have been carried out to study the mechanical performances of L-shaped CFT columns such as high strength, stiffness, good ductility. In the paper, Nine L-shaped CFT columns stiffened by binding bars and one without stiffeners subjected to eccentric-load are reported. The experimental results are compared with the results calculated by the abaqus. The proposed method provide theoretical basis for relative design codes.

Abstract: Insulating Concrete Forms (ICF) walls generally comprise two layers of Expanded Polystyrene (EPS), steel reinforcement is placed in the center between the two layers and concrete is poured to fill the gap between those two layers. ICF’s have many advantages over traditional methods of wall construction such as reduced construction time, noise reduction, strength enhancement, energy efficiency, and compatibility with any inside or outside surface finish. The focus of this study is the Screen Grid ICF wall system consisting of a number of beams and columns forming a concrete mesh. The performance of ICF wall systems under lateral loads simulating seismic effect is experimentally evaluated in this paper. This work addresses the effect of the different design parameters on the wall behavior under seismic simulated loads. This includes different steel reinforcement ratio, various reinforcement distribution, wall aspect ratios, different openings sizes for windows and doors, as well as different spacing of the grid elements of the screen grid wall. Ten full scale wall specimens were tested where the effects of the various parameters on wall behavior in terms of lateral load capacity, lateral displacement, and modes of failure are presented. The test results are stored to be used for further analysis and calibration of numerical models developed for this study.

Abstract: In this study, numerical simulations on the dynamic load-displacement behavior of typical RC columns under dynamic loadings considering the strain rate effect and the influence of shear deformation, geometrical nonlinearity, plastic hinge zone were performed with a dynamic fiber element model, where the dynamic constitutive model of concrete considering the strain rate effects proposed by the CEB-FIP code (1990) was employed. The developed dynamic fiber element models with and without the consideration of shear deformation were employed to simulate the load-displacement behavior of RC column specimens with different shear span to depth ratios and under different loading speeds. The simulation results were compared with test measurements. Results show that difference between the simulation results with and without the consideration of shear deformation can be detected, especially for specimens with small shear span to depth ratios. The simulation results are closer to the test measurements for all of the specimens when shear deformation is considered. The shear deformation effect on the dynamic load-displacement behavior of short columns subjected to dynamic loadings is needed to be considered.