This research investigates the performance of double C-purlin sections used in the concrete-filled steel tube (CFST) beams system. A recycled-lightweight concrete was used as infill material to reduce the newly suggested composite beam's self-weight and cost. Up to 70% of the raw coarse aggregate was replaced with the expanded polystyrene beads and recycled aggregate concrete . Also, the strengthening performance of the suggested CFST beam was investigated using carbon fiber reinforced polymer (CFRP) sheets. A total of seven specimens of concrete-filled C-purlin tubular sections were tested under four-point loads, and additional 12 models were numerically analyzed using finite element software. The conducted failure modes, flexural strength, flexural stiffness , and energy absorption index are presented and discussed. The results confirmed that the recycled-lightweight infill concrete material has a slightly lower influence on the investigated CFST beams' flexural performance than those with normal concrete (less than 10%). Like the conventional CFST beams, the double C-purlin tubular beams filled with recycled-lightweight concrete showed a normal response to the CFRP's strengthening quality. Moreover, the flexural strength capacity and stiffness values obtained from the current analyses are analogous with those theoretically predicted using the existing methods, which achieved mean values of about 0.759 and 1.126, respectively, as average prediction mean values of these methods.

Performance of the novel C-purlin tubular beams filled with recycled-lightweight concrete strengthened with CFRP sheet

In order to investigate the bond behavior of preplaced aggregate concrete-filled steel tube (CFT-PAC) columns and the difference of bond behavior between CFT-PAC columns and normal concrete-filled steel tube (CFT-NC) columns, a total of 11 columns were prepared and the push-out tests were conducted. The experimental parameters included the type of concrete (preplaced aggregate concrete and normal concrete), concrete strength (C40, C50 and C60), cross-section dimension (D = 219 mm, 299 mm and 351 mm) and the thickness of steel tube (t = 6 mm and 8 mm). The results indicated that the CTF-PAC columns had a similar load-slip curves with CFT-NC columns. The bond stresses of the CFT-PAC columns were higher than that of the PAC-NC columns at the same concrete strength. Increasing compressive strength of PAC increased the critical bond strength and bond strength of CFT-PAC columns. With an increase of the L/D ratio, both of the slip corresponding to peak load and bond strength of CFT-PAC columns exhibited an increasing trend. A rise in the D/t ratio led to a decrease in the bond stress of CFT-PAC columns and an increase in slip corresponding to the peak load of CFT-PAC columns. The proposed bond stress-slip relationship model considerably matched the bond stress-slip relationship of CFT-PAC columns.

https://www.mdpi.com/1996-1944/13/2/300/pdf

Research on the Bond Behavior of Preplaced Aggregate Concrete-Filled Steel Tube Columns

The invention relates to a precast segment assembled concrete filled steel tube bridge pier based on bolted connection, and belongs to the field of bridge engineering. The precast segment assembled concrete filled steel tube bridge pier comprises joint embedded steel connecting parts, precast concrete filled steel tube segments, inter-segment connecting steel tubes and high-strength bolts, wherein each concrete filled steel tube segment comprises a concrete filled steel tube, inner stiffening ribs, reserved bolt holes and preset nuts; each joint embedded steel connecting part comprises an embedded steel tube, an end welding steel plate, inner stiffening ribs, outer stiffening ribs and reserved bolt holes; reserved bolt holes are formed in the two ends of each inter-segment connecting steel tube; the precast concrete filled steel tube segments are connected through the reserved bolt holes by depending on the inter-segment connecting steel tubes and adopting the high-strength bolts; and the precast concrete filled steel tube segments are connected with an upper bent cap and a lower bearing platform through the joint embedded steel connecting parts by adopting the high-strength bolts. The precast segment assembled concrete filled steel tube bridge pier has the characteristics of being high in compression resistance and shear bearing capacity, easy to industrially manufacture, convenient to construct, energy-saving and environment-friendly in use, and the like, can remarkably shorten the construction period of bridge piers, and provides a quick and effective solution for quick bridge construction in highly seismic regions.

Precast segment assembled concrete filled steel tube bridge pier based on bolted connection

The flexural strength of Slender steel tube sections is known to achieve significant improvements upon being filled with concrete material; however, this section is more likely to fail due to buckling under compression stresses. This study investigates the flexural behavior of a Slender steel tube beam that was produced by connecting two pieces of C-sections and was filled with recycled-aggregate concrete materials (CFST beam). The C-section’s lips behaved as internal stiffeners for the CFST beam’s cross-section. A static flexural test was conducted on five large scale specimens, including one specimen that was tested without concrete material (hollow specimen). The ABAQUS software was also employed for the simulation and non-linear analysis of an additional 20 CFST models in order to further investigate the effects of varied parameters that were not tested experimentally. The numerical model was able to adequately verify the flexural behavior and failure mode of the corresponding tested specimen, with an overestimation of the flexural strength capacity of about 3.1%. Generally, the study confirmed the validity of using the tubular C-sections in the CFST beam concept, and their lips (internal stiffeners) led to significant improvements in the flexural strength, stiffness, and energy absorption index. Moreover, a new analytical method was developed to specifically predict the bending (flexural) strength capacity of the internally stiffened CFST beams with steel stiffeners, which was well-aligned with the results derived from the current investigation and with those obtained by others.

Flexural Strength of Internally Stiffened Tubular Steel Beam Filled with Recycled Concrete Materials.

The axial compressive behavior of stone-lightweight aggregate concrete-filled steel tubular stub columns

A segment-assembled type pier column member with a steel-concrete composite structure includes a reinforcement tube embedded in a pile cap, wherein the reinforcement tube is connected with a bottom of a lower segment of a hollow steel tube pier and is poured with concrete, and pier columns in upper and lower segments are reinforced by means of segment connecting and being embedded with local reinforcing meshes. A steel cross beam is connected with an upper segment of the hollow steel tube pier in an assembled way. A pre-stressed tensioning duct is reserved between the steel cross beam and the pier column in the upper segment.

Assembled type pier column member with steel-concrete composite structure

A horizontal cyclic test was carried out to study the seismic performance of lightweight aggregate concrete filled steel tube (LACFST). The constitutive and hysteretic model of core lightweight aggregate concrete (LAC) was proposed for finite element simulation. The stress and strain changes of the steel tube and concrete filled inside were measured in the experiment, and the failure mode, hysteresis curve, skeleton curve, and strain curve of the test specimens were obtained. The influence of axial compression ratio, diameter-thickness ratio and material strength were analysed based on finite element model. The results show that the hysteresis curve of LACFST indicated favourable ductility, energy dissipation, and seismic performance. The LACFST failed when the concrete in the bottom first crushed and the steel tube then bulged, thus axial force imposed by prestressing was proved to be feasible. The proposed constitutive model and hysteretic model of LAC under the constraint of its steel tube was reliable. The bearing capacity and ductility of the specimen increase significantly with increasing thickness of the steel tube. The bearing capacity of the member improves while the ductility and energy dissipation performance slightly decreased with the increasing strength of the steel and concrete.

Behaviour of lightweight aggregate concrete-filled steel tube under horizontal cyclic load

The the utility model discloses a slip restricted type assembled buckling restrained brace component, including peripheral square steel tube, main effect is in order to give restraint mechanism of sliding and the spacing motor-driven effect of core cell, the limiting plate is used for retraining the core cell, prevents its pressurized bucking, motor-driven board, it is main for can freely sliding at the square steel tube, adjust the restraint position, the bolt mainly is for location limiting plate and motor-driven board, slides after avoiding the spotting the component includes spring and no adhesive material layer simultaneously. The utility model discloses having obvious differently with traditional buckling restrained brace component, reducing the soldered portion of component, give first place to with the assembled, the location is easily installed to the component, and the core cell is also easily controlled with the clearance between retraining, the outer repeatedly usable that retrains replaces the core cell simultaneously, can change core cell length and thickness size, and core cell restraint function can be satisfied through the mechanism of sliding to outer restraint, and whole member economy is convenient

Slip restricted type assembled buckling restrained brace

The invention discloses a detachable anti-buckling supporting member constrained by bolts. The detachable anti-buckling supporting member constrained by the bolts comprises a peripheral bolt positioning square steel tube, the bolts, a transition clamp plate, springs, reinforced ribbed plates and partial unbonded material layers. The main function of the peripheral bolt positioning square steel tube is to provide positioning for the bolts and support limiting for a core unit. The bolts are mainly used for constraining the core unit, so that the core unit is prevented from being buckled due to compression. The transition clamp plate is used for improving the constraining performance of the bolts. The detachable anti-buckling supporting member constrained by the bolts is obviously different from a traditional anti-buckling supporting member, the manufacturing complex degree is lowered, installing and positioning are easy by using the bolts to carry out constraining, the core unit is easy to center, a gap between the core unit and the constraint is very easy to control, back-and-forth deploying and retracting can be achieved, the manufacturing process of the member is easy to control, meanwhile, only the core unit needs to be replaced, the outer constraint can be reused, and the whole member is economical and convenient.

Detachable anti-buckling supporting member constrained by bolts

Disclosed is a prefabricated pier column member with a steel-concrete composite structure, comprising a reinforcing tube (2) buried in a pile foundation platform (1). The reinforcing tube is connected to the bottom of a lower section (3) of a hollow steel tube pier and is filled with concrete, and the upper and lower sections of the pier column are connected with each other via sections and are reinforced by a pre-buried local steel mesh. A steel beam (12) is connected to an upper section (8) of the hollow steel tube pier column in an assembly way. A pre-stressed tension duct is reserved on the steel beam and the upper section of the pier column. Disclosed is also a construction method for the prefabricated pier column member with a steel-concrete composite structure. The method can shorten the construction period, reduce the construction difficulties, and speed up the construction schedule. The connection mode used is safe, reliable and easy to control; and the advantages of compressive property of concrete and tensile property of steel are fully taken. The whole member has a good application prospect because it is cost-effective and convenient and the construction of which is simple and fast.

Yu Zhenpeng

Papers

Assembled type pier column member with steel-concrete composite structure

Behaviour of lightweight aggregate concrete-filled steel tube under horizontal cyclic load

Slip restricted type assembled buckling restrained brace

Detachable anti-buckling supporting member constrained by bolts

Prefabricated pier column member with steel-concrete composite structure