Research On The Axial Compressive Behavior Of Specific Concrete Hollow Block Masonry

Specific concrete hollow block(SCHB)for reinforced concrete block masonry is a kind of highly competitive wall materials of the modern masonry structure towards light weight and high strength.However,at present,the research on the mechanical properties in axial compression of SCHB masonry is relatively backward.Therefore,the axial compression performance of SCHB masonry is systematically studied by means of experimental research and numerical analysis in this thesis,to identify the failure mechanism of SCHB masonry under axial compression,accurately estimate the compressive strength,elastic modulus,peak strain,and other design indicators,and make up for the lack of uniaxial constitutive model in current masonry code.The main contents include:(1)The axial compression test was carried out in four groups of 24 standard specimens.Failure characteristics,basic mechanical properties and complete stress-strain curves were obtained.The micro-mechanical finite element models of SCHB masonry were established using ABAQUS software.And the accuracy of the model in simulating the axial compression performance of concrete special block hollow masonry was validated by comparison with the experimental results conducted by the author as well as published literatures.Based on the finite element model,the failure mechanism of SCHB masonry under compression was studied.The influence of mortar strength on the failure mode of the specimen was discussed,and the main geometric parameters such as vertical mortar,bond pattern,horizontal mortar joint thickness and high-to-thickness ratio on the axial mechanical properties of specimens were also systematically analyzed.Moreover,to account for the probabilistic behavior of masonry wallettes,four material parameters,consisting of the elastic modulus,Poisson's ratio,compressive peak strength,and tensile failure strength,were selected as random variables.A global sensitivity analysis based on the Latin hypercube sampling technique and Sobol' method was performed to quantify the sensitivity indices of the input random variables.(2)A database of compressive tests on SCHB masonry prisms and wallettes was reviewed and summarized from available literatures.A total of 257 average masonry compressive strength data points,representing the experimental results of 1326 individual prisms,were collected.The numerical techniques of artificial neural networks and adaptive neuro-fuzzy inference systems were utilized to predict the compressive strength of SCHB masonry prisms and wallettes.Three main influential parameters,namely the prisms' height-to-thickness ratio,the compressive strengths of concrete hollow blocks and mortars,were used as inputs to the models.The results obtained from the proposed models were compared with five international masonry design codes(GB 50003-2011,TMS 402,CSA S304.1,Eurocode 6,and AS 3700)and a model proposed by Sarhat et al.The comparison showed that the two proposed models have excellent prediction ability with insignificant error rates and perform better than the existing e mpirical models.(3)Based on the collected database,the effects of the block compression strength,mortar compressive strength,height-to-thickness ratio and horizontal mortar joint thickness on the masonry compressive strength were studied.On the basis of 167 axial compression test results carried out in several research institutes in China,the predictive capability of the formula in Chinese masonry code was assessed,and an accurate formula to estimate the compressive strength of concrete special block hollow masonry was developed.The reliability analysis to assess the safety of new proposed formula was conducted using design point method.The live load type,live-to-dead load ratio,effect of probability distribution of model error,structural safety class and discretization of wall thickness were considered when calculating the structural reliability of SCHB masonry walls in compression.It is found that the average reliability indices meet the target reliability index for second class safety grade structures which comprised the majority of building stock in China.The compressive strength of SCHB masonry has a negligible influence on structural reliability.However,reliabilities are slightly influenced by live-to-dead load ratio and highly sensitive to the probability distribution of model error.(4)Based on the current research at home and abroad,the existing stress-strain models for various types of masonry were reviewed.Through regression analysis of the experimental results obtained in this research and other studies,simple relationships between the elastic modulus and corresponding compressive strength were identified.The mortar compressive strength,masonry compressive strength and masonry elastic modulus were used to predict the peak strain.Furthermore,the parabolic expression proposed by Kent and Park was used as a basis to describe the nonlinear behavior.Moreover,the analytical model was developed for the nonlinear stress-strain relationship of SCHB masonry after calibration with experimental results.The performance of the model was evaluated by comparison with other existing models on the basis of experimental stress-strain curves obtained in the current study and further research literature.The analytical model proposed in the present study showed good agreement with the experiments,suggesting better performance than existing constitutive models along the descending branch.The proposed analytical model was considered suitable for use in the design and numerical analysis of SCHB masonry structures.