A new type composite dowel shear connector was proposed by introducing folded angles in the steel dowels. Four push-out specimens and two composite beam specimens were designed and experimentally studied. The structural behavior and failure mechanism of the composite folded dowel shear connection were investigated. The concrete failure was observed in both push-out and flexural tests, and the folded steel dowels were capable of yielding development. It is found that the bearing capacity and shear stiffness of the specimens with denser spacing dowels were higher than that of specimens with sparser dowels, but the ductility and deformation performance of the specimens with denser spacing dowels were lower than those with sparser dowels. By means of the finite element model simulation, the influence of strength and thickness of concrete slab, strength, thickness and folded angle of steel dowel on the mechanical properties of folded dowel shear connection were analysed. The folded angle could be determined as 20° because of the larger actual effective shear area and bearing capacity. Based on the bearing capacity analysis in terms of the three likely failure modes, such as steel failure, concrete shear failure and concrete pry-out, calculation formula of the shear bearing capacity of the folded dowel shear connection was put forward and verified. The calculated results by the proposed formula were in good agreement with the test results. For the composite beams, the calculated bending moments derived from the transformed section and the plasticity section methods were also in good agreement with the test values. It is suggested that the shear connection degree should be greater than 1 to enable a full composite beam.

In reinforced concrete (RC) structural systems, the use of ultra-high performance fibre reinforced concrete (UHPFRC) as an alternative to ordinary concrete is promising, especially in critical locations such as wet joints between prefabricated members. To better understand and guide construction practice of reinforced UHPFRC members, twenty-eight pull-out specimens were tested to investigate the bond performance of steel bars embedded in UHPFRC. The influences of embedment length and bar diameter were analysed and discussed. Due to the high cracking resistance of UHPFRC, no crack formation or splitting failure was found during the test. It is concluded that the bond development and deterioration process of steel bars in UHPFRC are fundamentally similar to those observed in ordinary concrete except for the higher initial bond stiffness and peak bond strength. Moreover, formulae for calculating normalized bond strength and residual bond strength were proposed, and an analytical model for bond stress-slip response was developed accordingly, based on a modification of the model recommended by fib Model Code 2010. Finally, suitable anchorage lengths of deformed steel bars in UHPFRC were discussed and suggested.

In reinforced concrete (RC) structural systems, the use of ultrahigh-performance fibre RC (UHPFRC) as an alternative to ordinary concrete is promising, especially in critical locations, such as wet joints between prefabricated members. To better understand and guide the construction practice of reinforced UHPFRC members, 28 pull-out specimens were tested to investigate the bond performance of steel bars embedded in UHPFRC. The influences of embedment length and bar diameter were analysed and discussed. Owing to the high cracking resistance of UHPFRC, no crack formation or splitting failure was found during the test. It is concluded that the bond development and deterioration process of steel bars in UHPFRC are fundamentally similar to those observed in ordinary concrete except for the higher initial bond stiffness and peak bond strength. Moreover, formulae for calculating normalised bond strength and residual bond strength are proposed, and an analytical model for bond stress–slip response has been developed accordingly, based on a modification of the model recommended by fib Model Code 2010. Finally, suitable anchorage lengths of deformed steel bars in UHPFRC are discussed and suggested.

Orthotropic steel-UHPC composite deck consists of orthotropic steel deck and ultra-high performance concrete (UHPC) layer. The shear force transferred by shear studs at the interface between steel deck and the UHPC layer is a key in fatigue design. Based on the finite element (FE) whole model analysis of composite deck, the detailed submodels of composite deck segments with single stud and single row studs were established respectively. It aimed to investigate the interface stress distribution and slip behavior of steel-UHPC composite deck under negative bending moment, and explore the failure mechanism of short headed stud. In term of shear force relationship, considering likely influences such as location and pattern of loading, flexural stiffness of the composite deck and stud arrangement, the whole model analysis results were compared with the submodel analysis results, and a fitting formula of shear relationship between the two models was proposed. A formula for fatigue design of short headed stud in orthotropic steel-UHPC composite deck was also proposed. In respect to the longitudinal and transverse shear force distribution of studs, composite deck stiffness, hot spot stress of fatigue-prone details of steel bridge deck and the maximum stress level of UHPC layer, the evaluation method of stud arrangement was proposed. The calculation results were assessed and compared with the stud layout schemes of three actual steel-UHPC composite decks, and the effectiveness of the design formula was validated.

Ultrahigh-performance concrete-orthotropic steel composite bridge deck is composed of the orthotropic steel deck and a thin ultrahigh-performance concrete (UHPC) overlayer. In the previous fatigue tests, two typical fatigue failure modes were found and identified. As a supplementary test after fatigue tests, air penetration method is capable of providing a reference to the quantitative and non-destructive damage detection of fatigue damage of UHPC. To further the previous study, a detailed numerical investigation is accomplished through complimentary finite element (FE) analysis. Compared with the solid element model, the refined shell-solid element model can better reflect the mechanical behavior. It is illustrated that the vertical stress can be adopted in assessing the fatigue strength of rib-to-diaphragm welded connection in the field test by means of nominal stress method. The combination of various factors would lead to fatigue shear failure of the short headed-studs. The fatigue strength of rib-to-diaphragm welded connection predicted by the hot spot stress method and the consistent nominal stress (CNS) method can basically meet the requirements of FAT90. The consistent nominal stress method can be used as the optimization method of nominal stress of fatigue detail. It is demonstrated that the fatigue life of UHPC can be estimated by S-N curves of ordinary concrete conservatively. The allowable equivalent maximum stress level can be taken as 0.55 for two million cycles of fatigue loading, and 0.52 for five million cycles of fatigue loading.

In the UHPC-steel composite bridge deck, the thickness of UHPC layer is usually only 40-50 mm, so short headed studs are used for shear connection of the interface between UHPC and steel deck. In this paper, the refined finite element (FE) model of push-out specimen is established to explore failure mode of the stud connection, damage concentration location of UHPC and load-slip behavior of UHPC-steel interface. Verified against the existing test results, FE parameter analysis is conducted, and shear strength formula and load-slip relationship of short headed stud embedded in UHPC are proposed. With the consideration of reduction effect of group studs, the shear strength formula of single stud can be used to simplify the calculation safely. A nominal shear stress S-N curve with 95% survival probability is proposed, fitted by the International Institute of Welding (IIW) recommended method. Based on the fracture mechanics method, a fatigue life evaluation formula of stud under influence of multiple factors is established. By the comparative analysis between the proposed formulas and the existing codified formulas for stud connection in ordinary concrete, the recommended formula for the fatigue strength of stud in UHPC is proposed.

Ultra-high performance concrete filled steel tube (UHPCFST) column is an innovative and efficient structural member, especially suitable for applications requiring high load carrying capacity. This paper experimentally and numerically investigated the structural behavior of UHPCFST columns under eccentric compression, which was a continuation of the previous program regarding axially loaded members. A total of twenty specimens with circular section (CS) and square section (SS) were tested, including twelve specimens under eccentric compression and eight specimens under concentric compression as reference. The eccentric compression characteristics of UHPCFST columns were analyzed and discussed, including failure mode, load versus lateral deflection relationship, load bearing capacity and the development of bending moment and curvature. Finite element (FE) analysis was conducted to predict the behaviors of the test columns and to select a suitable numerical model for UHPC under confining pressure. Finally, the feasibility of existing design codes for predicting the load bearing capacity of UHPCFST columns under eccentric compression was evaluated.

UHPC-orthotropic steel composite deck is an innovative and efficient bridge deck system, however the failure mode of this composite bridge deck under fatigue load is still not well understood, particularly when the deck is in hogging bending. To investigate the fatigue behavior of the UHPC-orthotropic steel composite deck, two multi-span full scale composite bridge decks in hogging bending were experimentally studied. To simulate the bridge deck under negative bending, the specimens were designed with the mid-span deck simply supported and two overhanging decks each side. Each specimen was tested twice. In the first test phase, the specimen was loaded with a vertical force acting on one side span, while in the second test phase, the specimen was vertically loaded on another side span. Tests revealed that among the all fatigue-prone details of an orthotropic steel deck, only the longitudinal cracks were observed occurring in the low portion of rib web which was near the weld toe of the rib to the transverse diaphragm. The fatigue strength of these specific cracks longitudinally orientated can be evaluated in a term of the vertical stress range of the rib below the weld toe under the fatigue details category C of AASHTO or category 71 MPa of Eurocode3. Shear connection failure of the composite deck was also found featuring with delamination between UHPC and steel bridge deck. Fatigue damage of the short headed studs was further inspected and evaluated by means of drilling test. It is found that the fatigue life of the shear connection is governed by the fatigue shear strength of the short headed studs, which is much longer than the fatigue life codified in the specifications for studs of conventional composite beams. The fatigue shear connection strength of the composite bridge deck can be assessed conservatively in a term of the fatigue shear strength of the headed studs.

The welded and bolted splice plate connections in orthotropic steel decks (OSD) are prone to fatigue problems resulting from the high cyclic stresses. An experimental study was conducted to investigate the fatigue behavior of U-rib connections. Four OSD specimens, two with butt-welded connections, and two with bolted splice plate connection were experimentally studied. For the U-rib welded connections, fatigue cracks were first observed on the outside bottom in the connection welds and propagated along the welds in the two side webs of the ribs approaching up to the deck plate. For the bolted splice plate connection, vertical cracks were first observed at the bottom of the inside splice plates. Cracks were then observed on the outside bottom in the connecting plates and propagated upward, and finally separated the splice plate completely. The test results were evaluated and compared to the existing codified S–N curves. The fatigue strengths of two connections are found in the category C of AASHTO (89 MPa) and category 90 MPa of EUROCODE. The finite element models of the U-rib connections were developed and verified by the test results. Parameter analyses were further conducted to investigate the likely influences of the fatigue behavior. For the welded connection, increasing the rib thickness, reducing weld size and adopting smooth weld shape can reduce the stress of butt-welded joints. For the splice plate connection, using thicker and wider splice plates can effectively reduce the fatigue stresses of the joints, hence improve the fatigue strength of this type U-rib connection.

This paper presents an earthquake-resistance study program of a long-span cantilevered story building. The program consists of a shaking table test study and nonlinear seismic analysis using finite element modeling technique. A 1/30 scale model of the prototype structure was designed and manufactured and then tested via the shaking table facility. Dynamic responses of the prototype structure under different earthquake excitation loadings were simulated. Dynamic properties, acceleration, and deformation responses of the scale down model under different intensity levels of earthquake were studied. The dynamic behavior, cracking pattern, and the likely governing failure mechanism of the structure were analyzed and discussed as well. The seismic responses of the prototype building were deduced and analyzed in terms of the similitude law. Furthermore, elaborate finite element models were established, and nonlinear numerical analysis of the prototype structure was conducted. The errors in the seismic response of the structure caused by structural simplification of scale down modeling are found small, and the dynamic behavior of the structure was not altered in the earthquake excitations. This test study provides a benchmark to calibrate the finite element model and a tentative guide in seismic design of such long-span cantilevered story buildings.

Steel tube filled with ultra-high performance concrete (UHPCFST) is an innovative and efficient structural form. To promote its application, a comprehensive experimental program was conducted to investigate the structural behavior of UHPCFST columns subjected to axial compression. The key issue is to clarify the differences in mechanical behavior between UHPCFSTs and CFSTs, and to evaluate whether the current design guidelines related to CFSTs are applicable to UHPCFSTs. To address this, the compression characteristics of UHPCFSTs were analyzed, including failure mode, load versus deformation relationship, axial compressive strength and strain development. The test results showed that the steel tube and UHPC worked well together, but the enhancement effect of the steel tube on the core UHPC strength was not as significant as that of ordinary concrete. Moreover, an experimental database of UHPCFSTs including this study was established, and the experimental results were compared with the predictions by various design codes. Based on the regression analysis of the database results, a simplified model for predicting the ultimate strength of UHPCFSTs was developed. It was concluded that the proposed model could accurately predict the axial compressive strength of UHPCFSTs with circular and square cross-sections, and was also applicable to UHPCFSTs with high-strength steel (HSS).

This paper proposes an innovative connection known as double-through plate connection, in which two plates pass through a slotted square column with the concrete infill. The type of connection can be used to connect the steel hollow structural section (HSS) beam to the concrete-filled steel tube (CFST) column. Three specimens were tested under cyclic loading. The failure modes, hysteretic performance, stiffness, strength, ductility and classification of the joints were evaluated. The results revealed that the type of connection exhibited similar behaviors with single plate connection. The characteristics of the connection effectively reduced the stress level on the column flange and improved stress distribution. Then a nonlinear finite element (FE) model was developed and verified by the experimental results in terms of moment-rotation relationship and failure mode. The parametric analyses were utilized to explore the effect of hole shape and bolt pretension force on the connection performance. In addition, bolt slippage and load transfer mechanism in the joint region were also discussed.