| The steel-reinforced concrete(SRC)composite columns with the arrangement of full or partial encased steel sections in the concrete have attracted widespread attention because of their advantages compared to conventional reinforced concrete(RC)columns.In recent years,the SRC columns have been used in the medium and high-rise buildings.Important advancements have been made by the prior studies in the SRC composite columns under the axial load and push-out load.However,they focused fundamentally on the columns elements with the normal-simple arrangement of structural steel section,and insufficient attention was considered to the novel types of SRC columns with X-shaped structural steel sections whose steel sections'webs coincide on the corner to corner diagonal lines of the column's section.The lightweight concrete(LWC)is widely used in buildings due to its numerous advantages,and a lot of studies have been conducted to investigate the structural behavior of the LWC,but brittle failures are usually found,especially for higher strength concrete.Because of the lack of studies and columns'brittle failure with LWC and high-strength concrete(HSC),more studies are required to know the performance of the SRC columns with LWC and HSC,especially novel types of them,under different loading cases.The chapter of the literature review of this thesis aims to summarize and collect the previous representative publications regarding the SRC composite columns.The analytical-theoretical studies of the SRC composite columns,including comparative studies between the design available codes to address the designs'philosophy and the limits in the standards and design available codes,bond-slip behavior,analytical confinement material models of concrete,and numerical-finite element(FE)analysis,are addressed.Additionally,the summary and discussion of the axial performance of the SRC columns elements and the impacts of the important parameters influencing the axial performance of these novel kinds of columns were included.The chapter also attempts to cover most of the parameters affecting the lateral cyclic performance of the SRC composite columns.In this thesis,the axial performance of the new type of steel reinforced lightweight aggregate concrete(SRLWAC)columns with+shaped and X-shaped steel sections is experimentally studied.To get a better understanding of the new types of SRLWAC columns,to provide some design guide,and to know the performance criteria of these columns;the effects of LWAC strength(1)(8),steel section configuration,steel section ratio(?ss),one cycle of high-speed pre-loading,the steel stirrups ratio(?sv),longitudinal bars ratio(?sr)on the axial compressive behavior of the new types of SRLWAC column are experimentally investigated by testing nine new types specimens under monotonically-axial-compressive loads.From the results,it could be found that the specimens with larger?sv,1)(8),?sr,and?ss achieved great strength and stiffness due to the excellent interaction between the steel and concrete.The cross-shaped(+and X-shaped)steel section could effectively prevent the shear cracks,and the well-confined concrete core could prevent both the local and overall buckling of the steel section.The ductility(?)and toughness of the specimens was influenced by1(8),?ss,and?sr;besides,larger?sv with smaller1(8)led to better?and toughness.The load's transfer between concrete and steel sections largely depends on the1(8),and the ultimate capacity of the new types of SRLWAC columns could be approximately predicted,referring to the codes'formulas of ordinary types of SRC columns.Among the available seven used codes,the BS-5400-05 led to the most conservative results.Analytical models and FE analyses(using ABAQUS)for predicting the axial performance of the new types of the SRLWAC columns with cross-shaped(+shaped and X-shaped)steel sections are proposed,considering the effect of different parameters.The concrete damage plasticity(CDP)model is applied in the three-dimension(3D)FE numerical models.The stress-strain material models for different components in the columns,including the confined zones of the LWAC using three and four concrete zones divisions approaches and with or without taking into account the stirrups reaction effect,are established first.Then,the analytical models for determining the axial load-deformation behavior of the SRLWAC columns are drawn based on the materials models.The analytical and FE models'results are compared with the experimental test results of the axially loaded SRLWAC columns.The proposed analytical and FE models accurately predict the axial performance and capacities of the new types of SRLWAC columns with acceptable agreements for the load-displacement curves.The contact stress distribution between the steel section and concrete is studied.The analytical parametric studies are also studied,in terms of the effects of confinement,1((8),?ss,and?sr on the axial capacity of the SRLWAC columns.In order to examine the bond-slip performance for the new type of SRLWAC columns with innovative X-shaped steel sections,comprehensive studies,including experimental studies and theoretical analyses,are done.To provides an insight into the bond-slip experimental behavior under push-out loading and to validate the theoretical-analytical studies,the effect of shear connectors(SCs)presence.The effects of stirrups confinement(?sv)on the bond-slip behavior of the new types of SRLWAC column are experimentally studied.Force-slip curves,force axial and horizontal deformations,failure modes,and crack patterns of the column specimens were investigated;the force transfer,interface bond-stress,bond shear transmission length,and strains were calculated and discussed.The comparison between the bond strength of the new type of SRLWAC column and ordinary types column specimens with H or I-shaped steel sections from 13 previous experimental studies showed superior and excellent bond strength capacity for the specimens with X-shaped steel sections.Five related models of bond capacity were discussed,and the utility of the models was put forward.A simplified load-slip model was proposed and verified.To examine the effective parameters of the bond,the most feasible model and the simplified model were used in the parametric study.The outcomes showed that the geometric configurations and materials strength parameters affect the bond-strength capacity.The confinement and SCs have effects on the bond and failure mode.The natural bond-stress combined with SCs produced smaller bond strength than that from both natural bonds and using higher?sv.Finally,from this study and previous works,the study concludes with suggestions,recommendations,and the limitations for the future work studies and structural designers to enhance the usefulness of the composite SRC columns. |
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