Experimental study on ultimate flexural capacity of steel encased concrete composite beams

Based on the experimental study and inelastic theory, the ultimate flexuralcapacity of steel encased concrete composite beams are derived. The difference between steel encasedconcrete composite beams with full shear connection and beams with partial shear connection,together with the relationship between the inelastic neutral axis of steel parts and concrete parts,are considered in the formulae. The calculation results of the eight specimens with full shearconnection and the three specimens with partial shear connection are in good agreement with theexperimental data, which validates the effectiveness and efficiency of the proposed calculationmethods. Furthermore, the nonlinear finite element analysis of the ultimate flexural capacity of thesteel encased concrete composite beams is performed. Nonlinear material properties and nonlinearcontact properties are considered in the finite element analysis. The finite element analyticalresults also correlate well with the experimental data.

Properties and calculation of normal section bearing capacity of RC flexural beam with skin textile reinforcement

In order to overcome the wide crack of ordinary reinforced concrete (RC) at service stage which affects the service performance and durability of structures,a kind of concrete structure with skin textile reinforcement is proposed,namely a part of concrete cover of RC members is replaced by textile reinforced concrete (TRC).The flexural experimental results indicate that when the reinforcement ratios of steel bars are constant,compared with control beams,the average value of crack loads of the beams,whose reinforcement ratios of textile are 0.018%,0.036% and 0.055%,increases by 15.5%,20.4% and 31.1%,respectively,the average value of yield loads respectively increases by 12.5%,19.9% and 21.1% and the average value of ultimate loads respectively increases by 8.5%,26.0% and 44.0%,respectively.Considerable reduction in cracks width and spacing is observed for specimens with a TRC layer,and when the beams yield,the maximum crack width of the beam with textile stuck no sand and the beam with textile stuck sand is reduced by around 60% and 70%,respectively.Surface treatment of textile and mixing polypropylene fiber into fine grained concrete contribute to enhance the service performance of the flexural element.Embedding U-shaped hoop has almost no effect on the control of the crack width.Finally,the calculation method of ultimate bearing capacity of this flexural component with TRC layer was presented.Comparison between the calculated and the experimental values reveals satisfactory agreement,and the maximum error is no more than 6%.

Modeling the Flexural Carrying Capacity of Corroded RC Beam

Considering the change of bond strength between corroded steel and concrete,flexural carrying ca- pacity of corroded reinforced concrete (RC) beam was calculated.On the basis of the condition of equilibrium of forces and compatibility of deformations for the whole beam,a model for the prediction of flexural carrying capacity of the corroded RC beam was proposed.Comparison of the model's predictions with the experimental results published in the literature shows the practicality of the proposed method.

Ultimate flexural strength of normal section of FRP-confined RC circular columns

Numerical analysis is carried out to study the sectional properties of the fiber-reinforced polymer（FRP）-confined reinforced concrete（RC）circular columns. The axial load ratio, the FRP confinement ratio and the longitudinal reinforcement characteristic value are the three main parameters that can influence the neutral axis depth when concrete compression strain reaches an ultimate value. The formula for computing the central angle θ, corresponding to the compression zone, is established according to the data regression of the numerical analysis results. The numerical analysis results demonstrate that the concrete stress enhancement from transverse confinement and strain hardening of the longitudinal reinforcement can cause a much greater flexural strength than that defined by the design code. Based on the analytical studies and the test results of 36 large scale columns, the formula to calculate the flexural strength when columns fail under seismic loading is proposed, and the calculated results agree well with the test results. Finally, parametric studies are conducted on a typical column with different axial load ratios, longitudinal reinforcement characteristic value and FRP confinement ratios. Analysis of the results shows that the calculated flexural strength can be increased by 50% compared to that of unconfined columns defined by the code.

Plate reinforced square hollow section X-joints subjected to in-plane moment

The static test of 13 square hollow section(SHS) X-joints with different β and different types of plate reinforcement under in-plane moment in brace was carried out. Experimental test schemes, failure modes of specimens, moment-vertical displacement curves, moment-deformation of the chord, and strain strength distribution curves were presented. The effect of β and plate reinforcement types on in-plane flexural property of SHS X-joints was studied. Results show that punching shear of chord face disappears, brace material fracture appears and concave and convex deformation of chord decrease when either collar plates or doubler plates were welded on chord face. Moment-vertical displacement curves of all specimens have obvious elastic, elastic-plastic and plastic stages. As β increases, the in-plane flexural ultimate capacity and initial stiffness of joints of the same plate reinforcement type increase, but ductility of joints decreases. With the same β, the in-plane flexural initial stiffness and ultimate capacity of doubler plate reinforced joints, collar plate reinforced joints, and unreinforced joints decrease progressively. Thickness of reinforcement plate has no obvious effect on in-plane flexural initial stiffness and ultimate capacity of joints. As thickness of reinforcement plate increases, the ductility of reinforced X-joints decreases. The concave and convex deformation of every specimen has good symmetry;as β increases, the yield and ultimate deformation of chord decrease.

Experimental and Theoretical Study on the Flexural Behavior of Recycled Concrete Beams Reinforced with GFRP Bars

This paper experimentally investigated the flexural behavior of reinforced recycled aggregate concrete(RAC)beams reinforced with glass fiber-reinforced polymer(GFRP)bars.A total of twelve beams were built and tested up to failure under four-point bending.The main parameters were reinforcement ratio(0.38%,0.60%,and 1.17%),recycled aggregate replacement ratio(R=0,50%,and 100%)and longitudinal reinforcement types(GFRP and steel).The flexural capacity,failure modes,flexibility deformation,reinforcement strains and crack distribution of the tested beams were investigated and compared with the calculation models of American code ACI 440.1-R-15,Canadian code CSA S806-12 and ISIS-M03-07.The tested results indicated that the reinforcement ratio has great influence on the ultimate load,crack width and deflection of GFRP-RAC beams,the recycled aggregate replacement ratio has little influence on it.However,it was found that the reinforcement ratio has no obvious influence on the cracking load which was only related to the recycled aggregate replacement ratio.The average cracking load decreased by 5%and 15%as the recycled aggregate replacement ratio increased from 0 to 50%and 100%.For the steel-RAC beams,the ultimate load was found to be about 1/2 of the ultimate load of GFRP-RAC beam under the same condition and the trend of strain,deflection and crack width were different from GFRP-RAC beams.This is due to the different material properties of GFRP bars and steel rebar.On the other hand,the calculation results showed that ACI 440.1-R-15 and CSA S806-12 underestimated the ultimate load of GFRP-RAC beams.Moreover,the deflection prediction of GFRP-RAC beams by CSA S806-12 is relatively accurate compared with ACI 440.1-R-15 and ISIS-M03-07.As for the prediction of crack width,the results of ACI 440.1-R-15 prediction were in good agreement with the experimental results at the ultimate load,with the average value of 1.09±0.28.

Flexural behavior of textile reinforced mortar-autoclaved lightweight aerated concrete composite panels

To improve the deficiencies of prefabricated autoclaved lightweight aerated concrete(ALC)panel such as susceptibility to cracking and low load-bearing capacity,a textile-reinforced mortar-autoclaved lightweight aerated concrete(TRM-ALC)composite panel was developed in this study.One group of reference ALC panels and five groups of TRM-ALC panels were fabricated and subjected to four-point flexural tests.TRM was applied on the tensile side of the ALC panels to create TRM-ALC.The variable parameters were the plies of textile(one or two),type of textile(basalt or carbon),and whether the matrix(without textile)was applied on the compression side of panel.The results showed that a bonding only 8-mm-thick TRM layer on the surface of the ALC panel could increase the cracking load by 180%−520%.The flexural capacity of the TRM-ALC panel increased as the number of textile layers increased.Additional reinforcement of the matrix on the compressive side could further enhance the stiffness and ultimate loadbearing capacity of the TRM-ALC panel.Such panels with basalt textile failed in flexural mode,with the rupture of fabric mesh.Those with carbon textile failed in shear mode due to the ultra-high tensile strength of carbon.In addition,analytical models related to the different failure modes were presented to estimate the ultimate load-carrying capacity of the TRM-ALC panels.

Investigation of mechanical failure performance of a large-diameter shield tunnel segmental ring

The control criteria for structural deformation and the evaluation of operational safety performance for large-diameter shield tunnel segments are not yet clearly defined.To address this issue,a refined 3D finite element model was established to analyze the transverse deformation response of a large-diameter segmental ring.By analyzing the stress,deformation,and crack distribution of large-diameter segments under overload conditions,the transverse deformation of the segmental ring could be divided into four stages.The main reasons for the decrease in segmental ring stiffness were found to be the extensive development of cracks and the complete formation of four plastic hinges.The deformation control value for the large-diameter shield tunnel segment is chosen as 8%o of the segment's outer diameter,representing the transverse deformation during the formation of the first semi-plastic hinge(i.e.,the first yield point)in the structure.This control value can serve as a reinforcement standard for preventing the failure of large-diameter shield tunnel segments.The flexural bearing capacity characteristic curve of segments was used to evaluate the structural strength of a large-diameter segmental ring.It was discovered that the maximum internal force combination of the segment did not exceed the segment ultimate bearing capacity curve(SUBC).However,the combination of internal force at 9°,85°,and 161°of the joints,and their symmetrical locations about the 0°-180°axis exceeded the joint ultimate bearing capacity curve(JUBC).The results indicate that the failure of the large-diameter segment lining was mainly due to insufficient joint strength,leading to an instability failure.The findings from this study can be used to develop more effective maintenance strategies for large-diameter shield tunnel segments to ensure their long-term performance.

Novel empirical model for predicting residual flexural capacity of corroded steel reinforced concrete beam

In this study,a total of 177 flexural experimental tests of corroded reinforced concrete(CRC)beams were collected from the published literature.The database of flexural capacity of CRC beam was established by using unified and standardized experimental data.Through this database,the effects of various parameters on the flexural capacity of CRC beams were discussed,including beam width,the effective height of beam section,ratio of strength between longitudinal reinforcement and concrete,concrete compressive strength,and longitudinal reinforcement corrosion ratio.The results indicate that the corrosion of longitudinal reinforcement has the greatest effect on the residual flexural capacity of CRC beams,while other parameters have much less effect.In addition,six available empirical models for calculating the residual flexural strength of CRC beams were also collected and compared with each other based on the established database.It indicates that though five of six existing empirical models underestimate the flexural capacity of CRC beams,there is one model overestimating the flexural capacity.Finally,a newly developed empirical model is proposed to provide accurate and effective predictions in a large range of corrosion ratio for safety assessment of flexural failure of CRC beams confirmed by the comparisons.