Zhou Dao Lu

Modeling the Behavior of Insulated FRP-Strengthened Reinforced Concrete Beams Exposed to Fire

External bonding of fiber reinforced polymer (FRP) composites has become a popular technique for strengthening reinforced concrete (RC) structures all over the world. So far, very little information is available on the fire performance of FRP-strengthened concrete members. The analysis presented here aims to develop a nonlinear finite element (FE) model of FRP-strengthened RC beams exposed to fire. The analysis consists of two portions: the initial portion is the calculation of the transient temperature distribution and the second portion is the structural response analysis due to the effect of thermal and mechanical load. The proposed numerical analysis is validated against proving fire tests. The results indicate that the predicted temperatures and deformations are shown to agree to the tests satisfactorily.

Seismic Performance of RC Short Columns Strengthened with BFRP

BFRP has excellent strength, durability, thermal properties and economic cost. To test seismic performance of short columns strengthened with BFRP. Low cyclic loading test was conducted on one comparative short column and two RC short columns strengthened with BFRP. The test shows that short columns warped by BFRP show excellent failure modes, shear capacity, ductility and energy dissipation. As a new fiber reinforced plastic, BFRP has a good prospect in the area of seismic strengthening for its low cost and comprehensive mechanical properties.

Experimental Study on Specimens of Steel Secondary Beam Embedded in Reinforced Concrete Girder of Frame Structure

Test of two specimens (four different joints) of steel secondary beam embedded in reinforced concrete girder in frame structure and one specimen with steel cantilever beam embedded in reinforced concrete girder under static load were conducted. The steel beam up-flange was pulled out because of the concrete cracks caused by the moment, shear and torsion at the upper zone of the concrete beam near the steel beam end. Shear failure of the concrete beam and the top flange pullout failure are the most hazardous failure modes. Lacking restraint of concrete and the reinforcement of steel bar in the concrete slab and catenary action of restraint steel beam, the capacity of steel cantilever beam is much smaller than other beams. Load-slip curve of top flange of steel beam, load-rotation curve of the steel beam end are obtained through experiment. Primary calculation method of joints flexural capacity related to section size of composite steel beam, embedded depth of steel beam, flange width of steel beam embedded end, height of frame girder, is put up with. Analytical results of ABAQUS are shown as follows. Top flange pullout failure of steel beam is caused by the detachment of concrete and steel beam end, and the warp of the concrete slab near the support plays an unfavorable action on the performance of the steel beam. The end rotational angle of the steel beam with anchor bar is smaller than that without. The steel beam with shear connectors develops a smaller rotational angle and a higher load capacity.

Analysis on Defects Location during Rebar Pull-Out Test by Acoustic Emission Technique

To confirm precision of acoustic emission source localization technique and validate rationality of acoustic emission parameters setting in concrete detection, defects location in pull-out specimens during bond failure were monitored by the method of 3D localization technique. In the monitoring,formation and propagation of cracks calculated by localization algorithm agrees with the real situation. AE parameters proposed in the paper help to identify source location with high accuracy.

Experimental and Numerical Study on Seismic Performance of Flat Columns under Bilateral Cyclic Loading

In order to research seismic behavior of flat columns under bilateral cyclic loading with different angles, pseudo-static tests are conducted, which includes three 1:2 scaled flat columns. The height-width ratio of the column section is 5. And the loading directions are 00, 250 and 450 respectively. By observation of the test phenomenon and analysis of the data, the seismic performance of the columns including stiffness, skeleton curves, hysteresis curves, ductility and energy dissipation are obtained. Moreover, finite element program ANSYS is employed to simulate the bearing capacity of specimens. The research shows that with the loading angles increasing from 0 to 45, the strength of the flat column decreased gradually, while the ductility and energy dissipation capacity increase, and the failure mode changed from compression-shear to compression-bending. P-Δ effect becomes evident at lager values of loading angle. The compression-shearing curve of flat column complies with a heart-shape curve.

Fracture Behaviors of Post-Fire Concrete

nvestigations on the residual Mode-I fracture behaviors of concrete subjected to elevated temperatures were implemented in present research. Test specimens of the same dimensions, 230×200×200 mm, were exposed to ten temperatures varying from 20oC to 600oC. The wedge splitting method was employed to obtain the complete load-crack mouth opening displacement curves (P-CMOD) of the post-fire specimens, from which the initial fracture toughness Kini, the critical fracture toughness Kic and the fracture energy GF were calculated. The results demonstrated that Kini, Kic decreased monotonically with increasing heating temperatures Tm owing to the thermal damage induced by high temperatures; whereas GF sustained a hold-increase-decrease tendency with Tm for the energy dissipation of multi-cracks.

Crack Extension Resistance of Post-Fire Concrete

Wedge-splitting test is carried out in present research.Determination of the residual crack extension resistance curves (KR-curves) associated with cohesive force distribution on fictitious crack zone of complete fracture process is implemented. In each temperature, with the distribution of cohesive force along the fracture process zone, the residual fracture toughness KR (Δ̱) increases with increasing crack length Δ̱. Whereas the KR-curves decrease with increasing temperatures Tm for the thermal damage induced.

Equivalence between Two Fracture Methods

Two fracture parameters, i.e., the initiation fracture energy release GIcini and the unstable fracture energy release GIcun, are termed to distinguish the different crack propagation stages. Totally ten temperatures varying from 20oC to 600oC and the specimen size of 230×200×200 mm with initial-notch depth ratios 0.4 were considered. Wedge-splitting method is adopted to measure the loadcrack mouth opening displacement curves (PCMOD) and double-G fracture parameters are experimentally determined. In order to verify the feasibility of this model in post-fire concrete, the effective double-K fracture parameters converted by double-G fracture parameters using are compared with the double-K fracture parameters.

Fracture Energy of Post-Fire Concrete

Temperature influence on the residual Mode-I fracture behaviors of concrete was investigated in present paper. The test specimens were exposed to temperatures varying from 65oC to 600oC with their weight losses monitored. The wedge splitting method was employed to obtain the load-crack mouth opening displacement (P-CMOD) curves of post-fire specimens from which the fracture energy GF was calculated. It is demonstrated that GF sustains a hold-increase-decrease tendency with Tm. The fracture energy is closely related to the ultimate weight loss wu of the concrete and their relationship is also established.

Determination of Double-G Fracture Parameters of Post-Fire Concrete

Double-G fracture model was recently proposed based on the conception of energy release rate to describe the fracture behaviour on cracked concrete. Two fracture parameters, i.e., the initiation fracture energy release GIcini and the unstable fracture energy release GIcun, are termed to distinguish the different crack propagation stages undergoing during the whole fracture process in concrete. In present work, following the Double-G fracture model at ambient temperature, the residual Double-G fracture parameters of post-fire concrete is elaborately introduced. Totally ten temperatures varying from 20oC to 600oC and the specimens size of 230×200×200 mm with initial-notch depth ratios 0.4 were considered. Wedge-splitting method is adopted to measure the loadcrack mouth opening displacement curves (PCMOD) and double-G fracture parameters are experimentally determined.