Research On Shear Capacity Of Deep Beam With High-strength Lightweight Aggregate Concrete

The size of section,deadweight,seismic behavior and economical effect of deep beam can be significantly improved by using lightweight aggregate concrete(LWAC).But lightweight aggregate concrete processes a distinct brittleness due to its lower strength of aggregates,especially under shear failure.Simultaneously,ascribing to the complicated mechanism of shear failure,a commonly accepted calculation model for shear is not appeared yet.In this paper,works on establishment of database,experimental program,and development of models for struct effective coefficient were sequentially implemented,and a process that the microstructure and mechanical properties of materials-analysis on database-experimental program-verification of theoretical model was taken as the thread,by which the shear performance of LWAC deep beams were deeply studied on the views of materials and of members.The research contents are shown as follows:1.Considering influencing factors of LWAC,17 series of pull-out specimens using the grade 900 crushed shale ceramists were prepared to investigate the bond-slip behavior between deformed bars and the LWAC,in which the strength level of LWAC,diameter of bars,anchorage length and type of aggregates were taken into consideration.The analytical result shows that the bond behavior curves of LWAC are similar to that of NWC,the ultimate bond strength is higher than that of NWC,which means the strength of mortar is an important fact influencing the bond behavior of LWAC.2.The SEM images of specimens showed that an appropriate amount of silica fume appears to improve properties of ITZ,thus the interlocking action and the chemical bonding between aggregates and cement mortar can be strengthened.The difference in strength between ITZ and aggregates was decreased by the increase in strength of aggregates,thus weak faces occurred in both ITZ and aggregates,which is different from low strength LWAC and is the reason for the increase in strength of LWAC.3.An analysis based on existing models in database was conducted..The struct-and-tie model was modified by considering the concrete strength and the shear-span ratio,and the calculation of struct effective coefficient was developed.The effectiveness of modified model was verified by using test results.4.15 LWAC deep beams under shear force were experimentally investigated.Failure process,failure mode,force-displacement curves,the propagation of inclined crack,and capacity of specimens were analyzed.The result showed that:failure modes of LWAC deep beams consists of shear compression failure and inclined splitting failure,the shear compression failure was transferring to inclined splitting failure with an increase in shear-span ratio.The inclined angle of struct was decreased with an increase in shear-span ratio,thus the effectiveness of struct arch mechanism was declined,meanwhile the slope of load-deflection curve was decreased.Degradation of stiffness was significant,by which the ultimate shear capacity was determined.With increases in shear-span ratio and width of loading plates,the shear capacity of specimens was virtually improved,which means the width of the inclined struct section was increased.The height of size effect was increased by increasing the width of loading plates.5.12 struct isolation body from high-strength LWAC deep beams with different parameters under axial force were experimentally researched,in which the influence of failure mode and transvers reinforced ratio were especially studied.The failure of inclined struct basically consists of struct zone failure and node zone failure,with an increase in struct reinforcement ratio,the struct zone failure was transferring to node zone failure.6.Based on the experimental results,the relevance between the isolated body and the deep beam was investigated.The result showed that:existing typical models and the struct-tie model developed in this paper were capable of calculating and predicting the shear capacity of deep beams.But the effective coefficient developed by MCFT was no longer adapted to LWAC,and It was suggested that the effective coefficient need to be selected according to the shear-span ratio.7.The design method considering the reliability and transverse reinforcement is able to be employed in shear design of deep beams,but the transverse reinforcement need to be reasonably deployed according to the transverse reinforcement ratio.Based on the analysis of normal weight aggregate concrete's STM using the database,the adaptability of the struct effective coefficients to the LWAC was carefully studied by considering the characteristics of LWAC.Finally,the STM and the statistics were unified to propose a calculation model and the design method of LWAC deep beams.Research results achieved in this paper are theoretically and practically valuable for the promotion of LWAC's application,and for the study on shear performance of concrete.