Bolted Steel Plates Research Articles

Tensile behaviour of open-hole and bolted steel plates reinforced by CFRP strips

Abstract The behaviours of the open-hole and bolted plates in tension are fundamental in the mechanical assessment of the bolted connections. Regarding the rehabilitation of steel structures, however, the combined effects of bolted washer clamp-up and CFRP reinforcement on the tensile behaviour of the connection with laser cut holes have not been fully understood. This investigation aims to fill the gap by carrying out experimental tests and developing analytical model accounting for these effects. The test results show that the CFRP reinforced plates are failed by the rupture of CFRP and the steel-adhesive interface failure accompanied by CFRP delamination. Both failure modes can be correlated with two load-deformation characterizing curves. It is also found that the increase of the nominal tensile strength of the specimens can be enhanced significantly by the increase of the number of the CFRP layers and further moderately improved with the combined effect of the bolted washer clamp-up. Moreover, the yield load and residual deformability of the specimens can be significantly increased with the bolted washer clamp-up and greater bolt torque respectively. An analytical model taking into account the bolt torque effect and interfacial stress equilibrium has been developed to predict the strength enhancement effects of washer clamp-up and CFRP reinforcement on the open-hole plates in different failure modes. The proposed model has been verified to be effective in providing satisfactory strength ratio in contrast to test data.

Local buckling of bolted steel plates with different stiffener configuration

Local buckling may occur on the compressive edge of steel plates in bolted side-plated (BSP) beams, which usually leads to premature failure analogous to over-reinforced concrete beams. This paper presents the results of an experimental study of eight local buckling test specimens. The plate thickness, the bolt spacing, the configuration of longitudinal and transverse stiffeners is varied to investigate their influence on the overall buckling resisting performance of the bolted steel plates. Significant enhancement in term of both the buckling strength and deformability is observed as the increasing of the plate thickness and the decreasing of the bolt spacing. Further improvement is found when the longitudinal stiffeners of different sectional size are employed. However, the additional transverse stiffeners impose no beneficial effect to the overall buckling performance. The test results can provide benchmark data for further theoretical and numerical studies. A previous finite element analysis is also introduced and great compliance is found between the experimental and numerical results.

Cyclic response of I-shaped bridge columns with substandard transverse reinforcement

The cyclic response of a typical bridge column with I-shaped cross-section and substandard transverse reinforcement was investigated by means of experimental and analytical research. The amount of transverse reinforcement was sufficient to ensure adequate shear strength, but other requirements of the Eurocode 8/2 standard related to the confinement and buckling of the longitudinal bars were not fulfilled. Failure was brittle due to the buckling and rupture of the longitudinal bars, which caused a progressive reduction of strength. The results of the experiment showed that the requirements of Eurocode 8/2 (which are quite stringent) related to the minimum volumetric ratio and the maximum centre-to-centre distance of the stirrups along the column, as well as the maximum distance between the engaged longitudinal bars, are justified in the investigated case. It was demonstrated that improperly designed stirrup hooks can cause a significant reduction in the ductility capacity of the column.An attempt was made to strengthen the column using CFRP sheets. The strengthening was not straightforward. Two types of anchoring were investigated. The most efficient method of anchoring was based on the use of bolted steel plates. Due to the unfavorable dimension ratio of the column cross-section, the efficiency of the strengthening was limited.The results of the experiment were used in order to identify the most suitable numerical models. Two engineering numerical macro models were analysed: a fibre based beam with hinges model, and a Giberson’s model. In both cases agreement with the results of the experiment was fairly good, as long as the buckling of the flexural reinforcement was not pronounced, and substantial in-cycle strength degradation was consequently obtained. Some of the parameters (e.g. the ultimate deformation of the concrete in non-strengthened column) were calibrated according to the experiment, since the available models, reported in the literature, did not suit the investigated case. These parameters require further investigation.The methods included in Eurocode 8/3, which are used to estimate the properties of the strengthened column, were compared. The procedures for estimation of the ultimate deformation capacity were also compared with some methods proposed in the literature. In the investigated case the best simulation of the experiment was obtained when the Lam and Teng’s model of confined concrete was taken into account, together with a standard theoretical procedure for the estimation of the maximum chord rotation.

Strengthening Long Steel Columns of S-Sections against Global Buckling around Weak Axis Using CFRP Plates of Various Moduli

AbstractThe traditional Euler’s buckling theory of slender columns indicates that column capacity depends on flexural rigidity (EI), rather than material strength. As such, the availability of ultrahigh modulus carbon fiber-reinforced polymer (CFRP) plates, which could be much stiffer than steel, can offer a unique alternative for strengthening slender steel columns, in lieu of welding or bolting steel plates. In this study, twelve 2.6 m long S75×8 steel columns of 197 slenderness ratio that represents the upper limit permitted by code were tested under concentric axial loading using pin-ended conditions. The columns were allowed to buckle around their weak axes. CFRP plates were adhesively bonded to the flanges of the steel I-shape sections in nine of the columns. The main parameters studied were the level of initial out-of-straightness [length(L)/8,387 to L/1,020], CFRP modulus (168–430 GPa), CFRP reinforcement ratio (13–34%) and the length of CFRP plate (33–95% of L). The gain in axial strength due to ...

Longitudinal Partial Interaction in Bolted Side-Plated Reinforced Concrete Beams

Reinforced concrete (RC) beams strengthened with bolted steel plates on their side faces are known as bolted side-plated (BSP) beams. The performance of BSP beams is closely related to the longitudinal partial interaction caused by the longitudinal slip on the plate-RC interface. In this study, an analytical model for the longitudinal slip and partial interaction was developed, and formulas for the BSP beams under several simple loading conditions were developed. The superposition principle was also proven applicable to the analysis of longitudinal slip, thus can be used to analyse the BSP beams under complicated loading conditions. The results of a previous numerical study were extracted to validate the analytical model, and an example was then presented to illustrate the applicability of the theoretical approach. This study enhances the understanding of the behaviour of BSP beams, and provides an approach to consider the influence of longitudinal partial interaction in the BSP strengthening design.

Metallurgical evaluation of flaw indications in tie chord transition butt welds from the I-64 Sherman Minton Bridge

In September 2011, the I-64 Sherman Minton Bridge over the Ohio River between New Albany, IN and Louisville, KY was closed due to the detection of cracks in fracture-critical tie chord members. The bridge remained closed for over five months while non destructive testing and repairs were performed. Metallurgical evaluations were conducted by Applied Technical Services, Inc. (ATS) on 21 cores extracted from fracture critical members of the bridge. The cores were reported to contain rejectable indications as identified by visual inspection (VT), magnetic particle inspection (MT), ultrasonic testing (UT) and/or radiographic testing (RT). The purpose of this investigation was to determine the nature and cause of the flaws and if there was any evidence of active propagating cracks. Of the 21 cores examined, 11 contained surface flaws within the vertical butt welds or heat-affected zones. One core contained a major subsurface planar discontinuity. Five cores contained minor subsurface indications. The base metal properties were consistent with high yield strength, quenched-and-tempered low alloy steel, i.e. “T1 ® ”/ASTM A514. The weld metal properties were also consistent with low alloy steel. All flaws and other weld discontinuities observed both at and below the surface of the web members were associated with the original tie chord welds or subsequent early weld repairs. These flaws were formed during or shortly after welding while in the fabrication shop. Fracture mechanics calculations determined that at a critical flaw size, temperatures below 30° F (-1.1°C) could possibly result in failure of the bridge. Metallurgical analysis of the flaws revealed no evidence of active crack growth due to fatigue, corrosion fatigue or stress corrosion. The flaw surfaces exhibited intergranular separation along with mixed mode brittle and ductile features characteristic of hydrogen-induced cracking. The fracture critical members of the tie chords box girders were reinforced by bolted steel plates and the bridge placed back in service in February, 2012.

Shear transfer in bolted side-plated reinforced concrete beams

Reinforced concrete (RC) beams strengthened with bolted steel plates on their vertical faces are known as bolted side-plated (BSP) beams. The behaviour and performance of BSP beams are controlled by the arrangement of the steel plates and the interfacial slips caused by the shear deformation of anchor bolts due to shear force transfer. In this study, a nonlinear finite element model validated by available experimental results has been used to investigate the shear stress transfer in BSP beams. The effects of loading arrangements and the stiffnesses of RC beams, steel plates and bolt connections were investigated in detail by a parametric study. The results of this study shed light on the basic understanding of the internal shear transfer mechanism between steel plates and RC beams. A new design approach is also provided to help structural engineers in the determination of the shear transfer profile and the critical bolt shear force in the design of BSP beams.

Hysteretic behaviour of dissipative bolted fuses for earthquake resistant steel frames

One of the most recent trends in earthquake-resistant design of structures – damage control when these are subjected to severe earthquakes – led to the development of an innovative repairable fuse device for dissipative beam-to-column connections in moment resistant steel frames with composite beams. This fuse consists of a set of bolted steel plates, at the web and bottom flange, connecting the “I” beam profile stub to the beam element. The seismic performance of the proposed device was assessed through an extensive experimental campaign comprising twenty-four cyclic and two monotonic tests. Those tests were conducted on a set of three beam-to-column sub-assemblies with different fuse devices for each test. The tested devices varied in terms of selected geometric and mechanical parameters, such as the resistance capacity ratio and the geometric slenderness. The tests showed that the proposed devices were able to concentrate plasticity and to dissipate large amounts of energy through non-linear behaviour. Subsequently, two distinct design models are proposed to allow the computation of the resistance and stiffness of the fuses. The results of these design models were favourably compared with those from the experimental tests.

Numerical Simulation about Reinforced Concrete Beams Strengthened by Bolting Steel Plates

This paper presents a three-dimensional nonlinear finite elemental analysis about the reinforcement concrete beams strengthened by bolting steel plate. The contact effects between the steel plate with reinforced concrete beam surface was simulated by developing the contact elements. The effect of strengthening is analyzed and the effects of the deformation and stress distribution of anchor bolt on the failure mode were investigated. It is declared that this strengthening method can obviously improve the capacity and stiffness of beam, and the flexural deformation of anchor bolt is key problem inducing the failure of strengthened beam. This template explains and demonstrates how to prepare your camera-ready paper for Trans Tech Publications. The best is to read these instructions and follow the outline of this text.

Use of bolted steel plates for strengthening of reinforced concrete beams and columns

Reinforced concrete (RC) structures often need strengthening due to defective construction, having higher loads than those foreseen in the initial design of the structure, or as a result of material deterioration or accidental damage. The need for strengthening concrete structures has become a crucial problem not only in developed countries but also in China and other developing countries. The use of bolted steel plates to retrofit existing RC structural components has been proven experimentally and practically to be effective in solving the problem. In this article, experimental and numerical studies conducted at The University of Hong Kong on the strengthening of RC-coupling beams, floor beams, and columns using bolted external steel plates are summarised. Features and design principles of this strengthening method are discussed.

Numerical Analysis about Flexural Strengthening Reinforced Concrete Beams by Bolting Steel Plates

This paper presents a three-dimensional nonlinear finite elemental analysis about the reinforcement concrete beams strengthened by bolting steel plate, which is a new strengthening method by anchoring plate to beam surface but not using any glue to help bonding. The contact effects between the steel plate with reinforced concrete beam surface was simulated by developing the contact elements. The effects of the plate thickness and the collocation of anchor bolts were investigated. The damage evolution about variable collocation of anchor bolts were investigated. It is declared that the collocation of anchor bolts play an obvious effects on the flexural capacity of strengthened beams, but the plate thickness give a little influence on it.

Analysis of side-plated reinforced concrete beams with partial interaction

Existing reinforced concrete (RC) beams can be strengthened with externally bolted steel plates to the sides of beams. The effectiveness of this type of bolted side-plate (BSP) beam can however be affected by partial interaction between the steel plates and RC beams due to the mechanical slip of bolts. To avoid over-estimation of the flexural strength and ensure accurate prediction of the load-deformation response of the beams, the effect of partial interaction has to be properly considered. In this paper, a special non-linear macro-finite-element model that takes into account the effects of partial interaction is proposed. The RC beam and the steel plates are modelled as two different elements, interacting through discrete groups of bolts. A layered method is adopted for the formulation of the RC beam and steel plate elements, while a special non-linear model based on a kinematic hardening assumption for the bolts is used to simulate the bolt group effect. The computer program SiBAN was developed based on the proposed approach. Comparison with the available experimental results shows that SiBAN can accurately predict the partial interaction behaviour of the BSP beams. Further numerical simulations show that the interaction between the RC beam and the steel plates is greatly reduced by the formation of plastic hinges and should be considered in analyses of the strengthened beams.

Plate-strengthened deep reinforced concrete coupling beams

Many old reinforced concrete buildings in developed countries need to be strengthened due to the aging of construction materials, changes in functional use or new design loading requirements. In the present study, a series of experiments were conducted attempting to retrofit deep reinforced concrete coupling beams using a bolted steel plate. In addition to the control specimen, the other specimens were bolted with a steel plate on the side face to improve the shear strength and inelastic behaviour. A mechanical device was added to two specimens to restrain plate buckling. The study revealed that adding an external plate is an effective way to improve the shear capacity, energy dissipation and rotation deformability of deep reinforced concrete coupling beams. Moreover, the plate buckling-restrained specimen with a sufficient number of bolts in the anchor regions had a more stable response and better inelastic performance under reversed cyclic loads. These findings can help designers to a better understanding of this type of composite coupling beam.

Numerical Simulation of Bolted-Steel Plates Strengthened Coupling Beams

One reinforced concrete coupling beam and two strengthened reinforced concrete coupling beams by bolted steel plates are analyzed by nonlinear finite element method. Two-dimensional finite element model is employed with material nonlinearities and geometrical nonlinearities. A special ring region, which simulates the slip effect between concrete and steel plates, is developed an incorporated into the numerical analysis model. The load-displacement relationship, cracking/crushing type and steel plates internal are compared and found to be in good agreement with those in test.

Retrofit of Deep Concrete Coupling Beams by a Laterally Restrained Side Plate

The existing designs for deep reinforced-concrete (RC) coupling beams with low shear-span ratios and conventionally reinforced shear stirrups tend to fail in a brittle way with limited ductility and deformability under reversed cyclic loading. This paper aims to develop a new retrofitting method for existing deep RC coupling beams that can enhance the deformability and energy dissipation while maintaining flexural stiffness, improving the beams’ performance during an earthquake. Experiments were conducted to test four half-scale deep RC coupling beams with the same geometry and reinforcement layout but with different retrofitting schemes. One beam was tested without retrofitting to act as a control, whereas the others were retrofitted by a bolted steel plate with or without adding a buckling restraining device. This study reveals that the deformation and energy dissipation of the deep RC coupling beams retrofitted with restrained steel plates improved while the flexural stiffness did not increase. Moreover, by using laterally restrained steel plates, the specimens had better postpeak behavior, a more ductile failure mode, and better rotation deformability.

Behavior of strengthened reinforced concrete coupling beams by bolted steel plates, Part 2: Evaluation of theoretical strength

Composite beams using bolts to attach steel plates to the side faces of existing reinforced concrete (RC) coupling beams can enhance both their strength and deformability. The behavior of those composite beams differs substantially from the behavior of typical composite beams made up of steel beams and concrete slabs. The former are subjected to longitudinal, vertical and rotational slips, while the latter only involve longitudinal slip. In this study, a mixed analysis method was adopted to develop the fundamental equations for accurate prediction of the load-carrying capacity of steel plate strengthened RC coupling beams. Then, a rigid plastic analysis technique was used to cope with the full composite effect of the bolt group connections. Two theoretical models for the determination of the strength of medium-length plate strengthened coupling beams based on mixed analysis and rigid plastic methods are presented. The strength of the strengthened coupling beams is derived. The vertical and longitudinal slips of the steel plates and the shear strength of the anchor-bolt connection group is considered. The theoretical models are validated by the available experimental results presented in a companion paper. The strength of the specimens predicted from the mixed analysis model is found to be in good agreement with that from the experimental results.

Seismic behavior of strengthened reinforced concrete coupling beams by bolted steel plates, Part 1: Experimental study

An experimental study of five full-scale coupling beam specimens has been conducted to investigate the seismic behavior of strengthened RC coupling beams by bolted side steel plates using a reversed cyclic loading procedure. The strengthened coupling beams are fabricated with different plate thicknesses and shear connector arrangements to study their respective effects on load-carrying capacity, strength retention, stiffness degradation, deformation capacity, and energy dissipation ability. The study revealed that putting shear connectors along the span of coupling beams produces no significant improvement to the structural performance of the strengthened beams. Translational and rotational partial interactions of the shear connectors that would weaken the load-carrying capacity of the steel plates were observed and measured. The hierarchy of failure of concrete, steel plates, and shear connectors was identified. Furthermore, detailed effects of plate buckling and various arrangements of shear connectors on the post-peak behavior of the strengthened beams are discussed.

Unilateral buckling of elastically restrained rectangular mild steel plates

This paper considers the elastic unilateral buckling of rectangular mild steel plates that are restrained elastically and subjected to bending and axial actions. A variational formulation of the Ritz method using linear combinations of harmonic functions for the buckling deformations is used to establish an eigenproblem to determine the plate local buckling coefficients. The motivation for the study is the retrofit of reinforced concrete beams by gluing and then bolting steel plates to the sides of the beam. Such plates, when acting compositely with the concrete beam, are subjected to predominantly bending and axial actions which may cause unilateral local buckling. Whereas the bolts provide complete restraint against buckling at discrete points, the glue may also inhibit local buckling between these nodal points since it acts as a continuous elastic restraint. The influence of the glue stiffness, support conditions and plate proportions on the unilateral buckling of such plates are assessed.

Retrofitting reinforced concrete beams by bolting steel plates to their sides -Part 2: Transverse interaction and rigid plastic design

In a companion paper, tests on bolted side plated beams have shown that side plates can substantially increase the strength of existing reinforced concrete beams with little if any loss of ductility and, furthermore, induce a gradual mode of failure after commencement of concrete crushing. However, it was also shown that transverse interaction between the side plates and the reinforced concrete beam, that is vertical slip and which is a concept unique to side plated beams, is detrimental. Transverse interaction increases the forces on the bolt shear connectors and, hence, weakens the beam. It also reduces the ability of the composite plated beam to yield and, hence, to attain its full flexural capacity. The generic concept of transverse interaction will be described in this paper and the results used to develop a new form of rigid plastic analysis for bolted side plated beams which is illustrated with an application.

Retrofitting reinforced concrete beams by bolting steel plates to their sides -Part 1: Behaviour and experiments

A procedure has been developed for bolting steel plates to the sides of existing reinforced concrete beams which can be used to increase the shear strength of beams, increase the flexural strength of beams with enhanced ductility or with only a small loss of ductility, and increase the stiffness of beams in order to reduce deflections and crack widths. It will be shown in this paper, through a qualitative analysis and through the results of testing eight large scale beams, that standard rigid plastic analysis techniques which are commonly used in the design of reinforced-concrete, steel, and composite steel and concrete beams cannot be used directly to design composite bolted-plated reinforced-concrete beams. In the companion paper, quantitative procedures will be used to adapt the standard rigid plastic analysis techniques for this relatively new form of retrofitting.