Mechanical Properties And Calculation Method Of Flexural Capacity Of GRC For Prefabricated Cabin

In order to meet the growing demand for power and energy,and to speed up the construction of power grids,State Grid Corporation of China has vigorously promoted the modular construction of intelligent substations since 2013.The secondary equipment prefabrication cabin is its core product.Due to the long transportation distance,complex service environment and difficulties of maintenance,the secondary equipment cabin has high requirements for its raw materials.Compared with steel or traditional reinforced concrete,Glass fiber Reinforced Concrete(GRC)has the advantages of lower density,higher bending strength,stronger corrosion resistance and better toughness.Thus it is an ideal raw material for the production of prefabricated cabin.However,there are few studies on the theories of application of GRC to load-bearing structures,resulting in the lack of standards or specifications to be followed in the calculation of bearing capacity.In addition,the existing research is mostly based on Portland cement-based GRC materials.The attention of the sulphoaluminate cement based GRC material is insufficient.In view of this situation,this paper studied the cubic compressive strength,splitting tensile strength,elastic modulus,uniaxial compressive stress-strain relationship,bending load-deflection relationship and tensile stress-strain relationship of GRC materials for prefabricated cabin.And the calculation method of the normal section bearing capacity of rectangular beam is proposed.The main contents and conclusions of the study are as follows:(1)The effects of four factors(cement types,water-cement ratio,cement-sand ratio and glass fiber content)on the mechanical properties of GRC were studied.The results show that the cubic compressive strength and elastic modulus of Portland cement GRC are higher than that of sulphoaluminate cement GRC,and the water-cement ratio and cement-sand ratio have significant effects on cubic compressive strength and elastic modulus.The contribution of glass fiber to the compressive strength of the cube has the best amount,which has a certain negative impact on the elastic modulus.This indicates that the compressive strength and modulus of elasticity of the cube are mainly determined by the matrix,and the effect of the glass fiber is slightly smaller.The glass fiber content is approximately proportional to the splitting tensile strength,flexural strength and tensile strength,which shows that the glass fiber has a good effect of enhancing the crack resistance.The strength of the matrix has a certain influence only when the glass fiber content is low,which indicates that the water-cement ratio and the cement type may affect the tensile strength,flexural strength and tensile strength of the GRC by indirectly affecting the strength of the matrix.(2)The uniaxial compressive stress-strain curve of GRC is affected by the cement system,water-cement ratio and glass fiber content.The effect of the peak stress is the same as the cubic compressive strength.The peak strain of the Portland cement system GRC is greater than that of the sulphoaluminate cement system.When the water-cement ratio is lowered,the rate of change of the rising and falling sections of the curve increases.After the glass fiber production is increased,the rate of change of the rising and falling sections of the curve will be reduced,and the glass fiber can also play a role in limiting crack growth when the axial compression of the test piece is broken.(3)The GRC bending load-deflection curve and the tensile stress-strain curve show similar laws.Glass fiber can change the form of concrete bending and tension,and delay the breaking speed of the test piece.The flexural strength and tensile strength of Portland cement system GRC are higher than that of sulphoaluminate cement system,but the peak value should be changed little,the bending deflection is about 50%,and the compressive strain is about 17%.This indicates that the glass fibers can be slowly pulled out in the sulphoaluminate cement system,resulting in a lower rate of destruction.This may be related to the difference between the hydration products of the two systems.The effect of the mortar on the curve is not significant.(4)Based on the above research,the design values of GRC compressive strength,tensile strength and the method of elastic modulus which related to the calculation of bearing capacity of normal section are determined.The peak strain of GRC of different cement systems under uniaxial compression is proposed respectively.The fitting formula of the ultimate strain is given,and the uniaxial compressive stress-strain relationship of the GRC is given accordingly.Based on this,the calculation method of the normal section bearing capacity of rectangular beam is given,and the bearing capacity of the prefabricated roof slab is considered when considering the tensile strength of 0%,25%,50% and 100% GRC materials.The calculations show that the tensile strength of GRC material has a significant contribution to the bearing capacity,and the contribution is more obvious when the reinforcement ratio is lower.For prefabricated cabin,at a safety factor of 0.5,considering 50% of the GRC tensile strength is able to increase the bearing capacity by more than one time.(5)Based on the developed GRC material,the production process of the prefabricated cabin was formulated,and a feasible operation method was given for the formwork,raw materials,pouring and curing methods,which can be used as a reference for the production of the prefabricated cabin.