رفتار سازه های ساندویچ پانل های پیش ساخته غیرمعمول بارگذاری شده

Results of an experimental investigation to study the ultimate strength behaviour of precast concrete sandwich panels (PCSP) with steel truss shear connectors are reported. Six full-scale sandwich panels with variable slenderness ratio were cast and tested under eccentric loads. Deflection characteristics, variations of strains across the insulation layer, strains in shear connectors, crack appearance and propagation under increasing load were recorded and analysed. The role of the shear truss connectors in transferring load from the outer wythe (layer) to the inner and ensuring composite behaviour was also observed. Results obtained showed that all panels behaved in a fully composite manner under eccentric load till failure. The ultimate strength of the PCSPs was found to decrease non-linearly with the increase in the slenderness ratio. Because of the complex behaviour of PCSP due to its material non-linearity and the interaction between its various components, finite element analysis (FEA) was conducted. Comparison with test results indicated that the FEA closely estimate the wall strength and formulae based on reinforced concrete principles underestimate the wall strength.

Concrete sandwiched insulated wall panels (PCSP) have recently become more widely used in the building industry in Malaysia due to their economical advantages, superior thermal and structural efficiency. PCSP consists of two layers of concrete called wythes separated by a layer of insulation. The concrete wythes are connected to each other by concrete webs, steel connectors or a combination of the two. A typical PCSP with a truss type shear connectors is shown in Fig. 1. Depending on the extent of composite action, the PCSPs can be non-composite, partially composite, or fully composite. To take full advantage of the strength of the two wythes, and to prevent individual wythe buckling, the shear connectors should be designed to provide for full shear transfer between the two concrete wythes. A technical definition of the percent of composite action is not well established in the literature [1], [2], [3], [4], [5], [6], [7] and [8].The complex behaviour of PCSP due to its material non-linearity, the uncertain role of the shear connectors and the interaction between its various components has led researchers to rely on experimental investigations backed by simple analytical studies. The scarcity of information on the behaviour of this important type of construction is due to the high cost of full scale testing and the extreme difficulty of fabrication of small-scale models. Furthermore, many sandwich panels in use in the North America and Europe are proprietary and the producers are thus reluctant to share information with their competitors [8] and [9]. In the majority of the compression loaded members, the loads do not act ideally at the centroid of the members (i.e. loads act eccentrically). The accidental eccentricity specified by the code (BS8110 Part: 1, 1997) [10] is not to be less than t/6 or 20 mm. In the present eccentric load tests, the load was applied at an eccentricity of 40 mm so that the panels were subjected to high bending moments. The aim of this paper is to investigate experimentally and theoretically the ultimate strength behaviour of the PCSP under eccentric load and study the impact of slenderness on its load bearing capacity, as the proposed PCSP is designed for use in low rise residential and office buildings.

The performance of six PCSP specimens with slenderness ratio varying from 10 to 20 subjected to eccentric load were presented. The test results were analysed in the context of load bearing capacity, load–deformation profiles, load–strain curves, cracking patterns and the mode of failure. It was observed that all test panels ultimately fail by crushing. It was noticed that the first cracks occurred at about 38–55% of the failure loads. It was also found that the failure modes of the six panels showed separation of the two concrete wythes near the upper part of the wall. The load bearing capacity of the panels was found to decrease non-linearly with the increase in the slenderness ratio. The decrease in the strength was about 38% for an increase of the slenderness ratio from 10 to 20 of H/t. It was found that the strains in shear connectors remained well below the yield strain and the panels were found to behave in a fully composite manner till failure. A comparison between the ultimate eccentric loads and the corresponding ultimate moments as determined using conventional approach based on reinforced concrete principles, the FEM obtained values and values obtained experimentally were made. It was found that The FEM results and results obtained from the experimental investigations were found in good agreement. However, classical expressions based on reinforced concrete principles underestimate the ultimate strength of the PCSPs.