Research On Behavior Of Precast Concrete Sandwich Panels With Steel-GFRP Composite Connectors

With the implement of assembled building with concrete structure and the implementation of building energy conservation and green construction,precast concrete structures have been more and more widely used.The precast concrete sandwich panel system(PCSP)has been widely popularized in the construction field because of its advantages of integration of structure(or enclosure)and thermal insulation and the same life as structure.It is the main development direction of building energy conservation wall in the future.Connectors,as an important component connecting inner and outer wythes,are the key factors affecting the structural and thermal properties of PCSPs.At present,there are two main types of connectors used in PCSPs: metal connectors and non-metal connectors.Metal connectors are firmly tied,but have more heat loss.Non-metallic connectors have less heat loss but lower shear strength and higher price.Therefore,it is urgent to develop new connectors with both mechanical and thermal properties to meet the structural and thermal performance requirements of PCSPs.Supported by the National Key Research and Development Program of China((2016YFC0701703)and Jiangsu Science and Technology Plan Project(SBE2017030853),this paper dedicated to develop a novel type of connector used in PCSPs,and systematically studied its mechanical properties and the structural and thermal performance of the PCSPs with this connector through experimental method and theoretical analysis.The main work and achievements are drawn as follows:1.A new type of connector is developed and named as steel-GFRP Copmosite Connector(SGCC).The connector is composed of steel bar and fiber reinforced composites.Small diameter ribbed steel bar or pretressed wire with spiral ribs is as the inner core,enclosed with GFRP composite resin layer and compounded by moulding process.The connector combines the advantages of steel bar and fiber reinforced composites.It has the advantages of high shear strength,low thermal conductivity,simple processing technology,mass production and convenient construction.2.Starting from the pull-out performance,the disk head and hooked SGCC of three different GFRP composites were compared with Thermomass MS and Spare III FRP rod connector under the same test conditions.The reasonable composite was selected to optimize and the SGCC was finalized.3.The pull-out and push-through tests were performed on a PCSP with finalized SGCC.The load-slip curves,ultimate tensile and shear bearing capacity and load-strain curves of the connectors are obtained.The failure modes and the influencing factors of mechanical properties were analyzed.The formulas for calculating the pull-out capacity of SGCCs based on the failure of concrete cones and the shear capacity of SGCCs based on the combination arrangement of straight insertion and oblique insertion are presented respectively,which are verified by the test results.According to the research results of mechanical properties of SGCC,the design method of SGCC system is put forward,which can be used as a reference for the layout design of connectors in PCSP.4.A full-scale experiment was conducted to investigate the effects of different layout schemes of SGCCs on the flexural and composite behavior of PCSPs under monotonic loads and wind-induced cyclic loads.The working mechanism of SGCCs is revealed,and the composite action degree of PCSPs at elastic stage and ultimate stage is estimated theoretically.The results show that the SGCCs can effectively transfer the interlayer shear force,and make the inner and outer wythes achieve a higher degree of composite action.The structural performance of the panels meet the design requirements and will not crack during service.It shows that the thinned PCSPs with SGCCs used in high-rise buildings are feasible.5.The thermal performance of PCSPs with SGCCs was tested.The influence of the number of SGCCs and the thickness of thermal insulation layer on the thermal performance of PCSPs is analyzed.The feasibility of thermal performance of SGCCs is determined.According to the thermal requirements of different building thermal design zones,the upper limit reference values of the number of SGCCs per square metre of sandwich panels with insulation layer of 50 mm and 90 mm thickness are given,which provide the basis for the design and construction of the connectors in PCSP.6.According to the above research results,the design method of PCSP with SGCCs is proposed.Taking a PCSP in a practical project as an example,the design process of SGCC system and PCSP system is given.The feasibility of thinned PCSP applied in practical project is verified by calculation.Finally,the performance research results of PCSPs based on SGCCs are summarized,and the key issues to be further studied are pointed out.