Beam Plastic Hinge Research Articles

Development of computing environment for the seismic performance assessment of reinforced concrete frames by using simplified nonlinear models

A computing environment for the seismic performance assessment of reinforced concrete frames has been developed in Matlab in combination with OpenSees. It includes several functions which provide calculations of the moment-rotation relationship of plastic hinges in columns and beams, rapid determination of simplified nonlinear structural models, the post-processing of the results of analyses and structural performance assessment with different methods. The user can add new functions to the PBEE toolbox in order to support additional procedures for the seismic performance assessment of RC frames, or can just change the rules for determining the moment-rotation relationship of plastic hinges in columns and beams, which are the main source of uncertainty in simplified nonlinear models. In the paper, the capabilities of the computing environment (PBEE toolbox) are first explained by focusing on the procedures for determining the moment-rotation relationship of plastic hinges. Different examples are then presented, starting with a comparison between the calculated response of a four-storey RC frame building and the response obtained in a pseudo-dynamic experiment. The calculated response was determined with the two different structural models which are later on used for the demonstration of the seismic performance assessment of the same structure by the N2 method. Lastly, seismic performance assessment of an eight-storey frame is performed by using incremental dynamic analysis with consideration of the modelling uncertainties.

Crack Pattern and Ductility of Steel Reinforced Ultra High Strength Concrete Composite Joint Subjected to Reversal Cycle Load

In order to investigate the seismic damage and performance of steel reinforced ultra high strength concrete composite joint subjected to reversal cycle load, six interior strong-column-weak-beam joint specimens were tested with various axial load ratio and volumetric stirrup ratio. A discussion on the crack mode and ductility was presented. It was found that all joint specimens failed in bending with a beam plastic hinge in a ductile manner, with crack propagation different from the weak-column-strong-beam joint. The experimental results indicated that test parameters of the steel reinforced ultra high strength concrete composite joint with good seismic performance may be referred for engineering application.

Cyclic behavior of steel I-beams modified by a welded haunch and reinforced with GFRP

Flange and web local buckling in beam plastic hinge regions of steel moment frames can prevent beam-column connections from achieving adequate plastic rotations under earthquake-induced forces. Reducing the flange-web slenderness ratios (FSR/WSR) of beams is the most effective way in mitigating local member buckling as stipulated in the latest seismic design specifications. However, existing steel moment frame buildings with beams that lack the adequate slenderness ratios set forth for new buildings are vulnerable to local member buckling and thereby system-wise instability prior to reaching the required plastic rotation capacities specified for new buildings. This paper presents results from a research study investigating the cyclic behavior of steel I-beams modified by a welded haunch at the bottom flange and reinforced with glass fiber reinforced polymers at the plastic hinge region. Cantilever I-sections with a triangular haunch at the bottom flange and flange slenderness ratios higher then those stipulated in current design specifications were analyzed under reversed cyclic loading. Beam sections with different depth/width and flange/web slenderness ratios (FSR/WSR) were considered. The effect of GFRP thickness, width, and length on stabilizing plastic local buckling was investigated. The FEA results revealed that the contribution of GFRP strips to mitigation of local buckling increases with increasing depth/width ratio and decreasing FSR and WSR. Provided that the interfacial shear strength of the steel/GFRP bond surface is at least 15 MPa, GFRP reinforcement can enable deep beams with FSR of 8-9 and WSR below 55 to maintain plastic rotations in the order of 0.02 radians without experiencing any local buckling.

Incremental dynamic analysis for estimating seismic performance sensitivity and uncertainty

AbstractIncremental dynamic analysis (IDA) is presented as a powerful tool to evaluate the variability in the seismic demand and capacity of non‐deterministic structural models, building upon existing methodologies of Monte Carlo simulation and approximate moment‐estimation. A nine‐story steel moment‐resisting frame is used as a testbed, employing parameterized moment‐rotation relationships with non‐deterministic quadrilinear backbones for the beam plastic‐hinges. The uncertain properties of the backbones include the yield moment, the post‐yield hardening ratio, the end‐of‐hardening rotation, the slope of the descending branch, the residual moment capacity and the ultimate rotation reached. IDA is employed to accurately assess the seismic performance of the model for any combination of the parameters by performing multiple nonlinear timehistory analyses for a suite of ground motion records. Sensitivity analyses on both the IDA and the static pushover level reveal the yield moment and the two rotational‐ductility parameters to be the most influential for the frame behavior. To propagate the parametric uncertainty to the actual seismic performance we employ (a) Monte Carlo simulation with latin hypercube sampling, (b) point‐estimate and (c) first‐order second‐moment techniques, thus offering competing methods that represent different compromises between speed and accuracy. The final results provide firm ground for challenging current assumptions in seismic guidelines on using a median‐parameter model to estimate the median seismic performance and employing the well‐known square‐root‐sum‐of‐squares rule to combine aleatory randomness and epistemic uncertainty. Copyright © 2009 John Wiley & Sons, Ltd.

Strengthening of reinforced high-strength concrete beam–column joints using advanced reinforcement details

Lack of ductility in high-strength concrete members raises serious concerns for overall structural safety, especially for reinforced concrete beam–column joints. In the current study, experimental research was performed to improve the seismic strength and performance of reinforced high-strength concrete exterior beam–column joints under cyclic load reversals. A new design approach for beam–column joints was introduced using advanced reinforcement details. Specimens of reinforced high-strength concrete beam–column joints were manufactured based on the new design method developed from the concept of a moving beam plastic hinge using anchor-type intermediate bars and advanced details of doubly confined closed stirrups in the beam near the joint, and tested for comparison with specimens designed using the conventional approach. The newly developed design approach minimised damage and considerably improved the structural performance of beam–column joints under cyclic load reversals. The manufactured joints were expected to be effective in improving the weakness induced by the brittleness of high-strength concrete in reinforced high-strength concrete beam–column joints.

A plastic collapse method for evaluating rotation capacity of full-restrained steel moment connections

An analytical method to model failure of steel beam plastic hinges due to local buckling and low-cycle fatigue is proposed herein. This method is based on the plastic collapse mechanism approach and a yield-line plastic hinge (YLPH) model whose geometry is based on buckled shapes of beam plastic hinges observed in experiments. Two limit states, strength degradation failure induced by local buckling and low-cycle fatigue fracture, are considered. The proposed YLPH model was developed for FEMA-350 WUF-W, RBS and Free Flange connections and validated in comparisons to experimental data. This model can be used to estimate the seismic rotation capacity of fully restrained beam-column connections in special steel moment-resisting frames under both monotonic and cyclic loading conditions.

철근콘크리트 보-기둥 내부 접합부의 전단 거동에 관한 실험적 연구

초록 · 키워드 목차 오류제보하기 등록된 정보가 없습니다. ABSTRACT1. 서론2. 철근콘크리트 보-기둥 접합부 실험3. 실험 결과 및 분석4. 결론참고문헌요약

Highly Damage-Tolerant Beam-Column Joints Through Use of High-Performance Fiber-Reinforced Cement Composites

//<![CDATA[ var theForm = document.forms['Form']; if (!theForm) { theForm = document.Form; } function __doPostBack(eventTarget, eventArgument) { if (!theForm.onsubmit || (theForm.onsubmit() != false)) { theForm.__EVENTTARGET.value = eventTarget; theForm.__EVENTARGUMENT.value = eventArgument; theForm.submit(); } } //]]>

Finite element methods for the analysis of softening plastic hinges in beams and frames

This paper presents new finite element methods for the analysis of localized failures in plastic beams and frames in the form of plastic hinges. The hinges are modeled as discontinuities of the generalized displacements of the underlying Timoshenko beam/rod theory. Hinges accounting for a discontinuity in the transversal and longitudinal displacements and the rotation field are developed in this context. A multi-scale framework is considered in the incorporation of the dissipative effects of these discontinuities in the large-scale problem of a beam and a general frame. A localized softening cohesive law relating these generalized displacements with the stress resultants acting at the level of the cross section is effectively introduced in the frame response. The resulting models, referred to as localized models, are then able to capture the localized dissipation observed in the localized failures of these structural members, avoiding altogether the inconsistencies observed for classical models in the stress resultants with strain softening. The constructive approach followed in the development of these models leads naturally to the formulation of enhanced strain finite elements for their numerical approximation. In this context, we develop new finite elements incorporating the singular strains associated to the plastic hinges at the element level. A careful analysis is presented so the resulting finite elements avoid the phenomenon of stress locking, that is, an overstiff response in the softening of the hinge, not allowing for the full release of the stress. The accurate approximation of the kinematics of the hinges requires a strain enhancement linking the jumps in the deflection and the rotation fields, given the coupled definition of the transverse shear strain in these two fields. Different enhanced strain elements, involving different base finite elements and different enhancement strategies, are considered and analyzed in detail. Their performance are then compared in several representative numerical simulations. These analyses identify optimally enhanced finite elements for the accurate modeling the localized failures observed in common framed structures.

Reinforced concrete edge beam—column—slab connections subjected to earthquake loading

Four two-thirds-scale reinforced concrete edge beam–column–slab subassemblies (two concentric and two eccentric connections) were tested under quasi-static cyclic lateral loading. Each subassembly represented a cruciform connection in an exterior moment-resisting frame with a monolithic floor slab on one side only, loaded in the longitudinal direction of the edge-beams. The tests explored the effect of eccentricity between beam and column centrelines, and the effect of floor slabs, on the structural performance of edge beam–column–slab connections subjected to earthquake loading. Performance of the specimens was evaluated in terms of overall strength and stiffness, energy dissipation, beam plastic hinge development, joint shear deformation, and joint shear strength. All specimens underwent some beam hinging at the beam/column interfaces. However, both eccentric specimens, and one concentric specimen with a heavily reinforced floor slab, eventually failed as a result of joint shear, whereas the other concentric specimen exhibited more ductile load–displacement response. The eccentric specimens (with different eccentricities and edge-beam widths) underwent similar behaviour before they started to break down, and they also reached similar joint shear strengths. Slab participation was evaluated using slab bar strain gauge data with respect to storey drift. Actual effective slab widths were much larger than the ones typically used in design, especially for the specimens with a column wider than the edge-beams. Finally, floor slabs imposed significant joint shear demand, but they also increased joint shear capacity by expanding effective joint width.

Reinforced concrete edge beam?column?slab connections subjected to earthquake loading

Four two-thirds-scale reinforced concrete edge beam–column–slab subassemblies (two concentric and two eccentric connections) were tested under quasi-static cyclic lateral loading. Each subassembly represented a cruciform connection in an exterior moment-resisting frame with a monolithic floor slab on one side only, loaded in the longitudinal direction of the edge-beams. The tests explored the effect of eccentricity between beam and column centrelines, and the effect of floor slabs, on the structural performance of edge beam–column–slab connections subjected to earthquake loading. Performance of the specimens was evaluated in terms of overall strength and stiffness, energy dissipation, beam plastic hinge development, joint shear deformation, and joint shear strength. All specimens underwent some beam hinging at the beam/column interfaces. However, both eccentric specimens, and one concentric specimen with a heavily reinforced floor slab, eventually failed as a result of joint shear, whereas the other concentric specimen exhibited more ductile load–displacement response. The eccentric specimens (with different eccentricities and edge-beam widths) underwent similar behaviour before they started to break down, and they also reached similar joint shear strengths. Slab participation was evaluated using slab bar strain gauge data with respect to storey drift. Actual effective slab widths were much larger than the ones typically used in design, especially for the specimens with a column wider than the edge-beams. Finally, floor slabs imposed significant joint shear demand, but they also increased joint shear capacity by expanding effective joint width.

Experimental Evaluation of Plate-Reinforced Steel Moment-Resisting Connections

Five cover-plate and five flange-plate single-sided steel moment-resisting beam–column assemblies were tested at full scale. Grade 50 steel was used for the W14×176 columns, the W30×99 beams, and all reinforcing plates. The procedures of FEMA 267A were used to design and detail the connections that included rectangular-, trapezoidal-, and swallowtail-shaped reinforcing plates. Cyclic and near-field loading histories were used to test the connections. None of the ten connections failed in a brittle manner; the strength of each connection degraded slowly due to local buckling of the beam web and flanges. The maximum beam plastic hinge rotations ranged between 2.3 and 3.9% rad. The cover-plate and flange-plate connections performed equally well but neither connection was subjected to large plastic strains at the face of the column. The performance of the tested plate-reinforced connections was best when rectangular reinforcing plates and three-sided fillet welds joining the reinforcing plate to the beam flange were used. Bracing of the beam bottom flange outside the plastic hinge zone to delay lateral-torsional buckling did not produce any significant improvement in connection hysteresis. Increased beam web compactness (smaller height to thickness) delayed the loss of strength and stiffness in the beam–column connection.

An assessment of parameters describing the response of a reinforced concrete beam

This paper outlines the background to a variety of parameters that are considered in order to establish their suitability as performance descriptors. This assessment is made in conjunction with data collected from twelve tests on nominally identical beam plastic hinges that were tested using different loading histories. Candidate descriptors are categorised as those that consider displacements and those based on damage. A suite of damage indices is also considered. Preliminary comments are made regarding the response comparison of tests conducted using different loading histories.

Reinforced Concrete Wide-Beam Construction vs. Conventional Construction: Resistance to Lateral Earthquake Loads

Experiments and analyses were conducted to address concerns about performance of reinforced concrete connections with shallow, wide beams subjected to lateral earthquake loading and to compare behavior of wide beam connections to that of conventional connections. Two wide beam-column-slab connections and one conventional beam-column-slab connection were subjected to cycles of reversing lateral displacements up to 5% drift. The conventional beam and wide beam connections exhibited similar overall load-displacement behavior, with similar beam plastic hinge development. The wide beam connections dissipated almost as much energy as the conventional beam connection and had greater slab participation and less joint and beam shear cracking than the conventional beam connection. Experimentally determined wide beam connection stiffness was closer to the conventional beam connection stiffness than had been predicted. Refined models were developed, with features such as rigid end offsets for wide beam connections, to better represent observed behavior. Nonlinear models were also developed that accurately captured differences in energy dissipation as well as stiffness.

Influence of loading history on the response of a reinforced concrete beam

An investigation considering the influence of loading histories on the performance of a reinforced concrete beam plastic hinge is described. Twelve loading histories were considered, including conventional procedures employed in the United States, Japan and New Zealand, and artificially generated histories derived from recorded earthquake ground motions. Details of the prototype structure and the test beam are described, followed by comprehensive reporting o f experimental data. Performance descriptors and further treatment of the experimental data are presented in a companion paper.

General report on local ductility

A series of factors contributes to the poor local ductility of steel structures, which was observed during recent earthquakes in the USA and Japan. These factors are explained. The factors on the resistance side are the discrepancies between real and design yield stress, the value of through thickness resistance of steel, the need for requirements on toughness of the base and weld material and the effect of strain rate. On the action effect side, other factors contributed to a bad ductility: the past underestimates of needed plastic rotations, the existence of 3D stress states created in welded connections of high beams, the consideration of wrong stress distributions in beam ends, a bad design of connections and the influence of the composite character of beams. The recent trends aiming at an improved local ductility are explained. They consist in forcing the development of plastic hinges in beams of moment frames to take place away from the columns, by either a connection strengthening or a beam weakening. Qualified connections are being developed. The other connections should go through a severe qualification process. However, future research work could relax this request by developing explicit requirements on the connections themselves.

Seismic Behavior of Composite RCS Frame Systems

This paper presents the results of an experimental investigation into the seismic performance of a composite moment resisting frame system that consists of reinforced concrete columns (with an embedded steel shape for erection purposes) and composite steel beam-reinforced concrete slab sections. Quasi-static reversed cyclic loading was performed on six two-thirds-scale subassemblage specimens. Various detailing options were evaluated to provide full moment connection in both orthogonal framing directions at the beam-column joints. With appropriate joint detailing, specimens exhibited a desirable beam plastic hinge mechanism with stable hysteretic response. Composite beam sections maintained near full composite behavior beyond code based drift limits with good energy dissipation characteristics and were able to undergo large plastic rotation magnitudes. This framing system may represent a viable alternative for low-to-mid-rise structures in high seismic risk zones.

Behavior of HPFRC Connections for Precast Concrete Frames Under Reversed Cyclic Loading

Describes the development of a high energy absorbing joint for precast/prestressed concrete structures in seismic zones. The joint acts as an energy dissipating connector between the beam and column elements. The material of the joint is a high performance fiber reinforced cement composite (HPFRC) matrix. Thirteen joint/ connection specimens were tested with the objectives of devising a reinforcement scheme for locating beam plastic hinges inside HPFRC cast-in-place connections, investigating the effect of different design parameters on the stability of the hysteretic response of the connections, and determining the reduction of transverse reinforcement in the connection by using steel fibers in the connection matrix. The performance of the connection was evaluated in terms of the failure mode, connection strength, displacement and rotation ductilities, connection flexural and shear deformations, energy dissipation, and loss of stiffness due to cyclic loading.

Discussion: Cause of Deformed Shapes in Cooling Towers

stituted. The basis of the 70% of full confinement referred to previously is that the amount of transverse confinement with result in 4>ul4>y of at least 10 being attained. Also, in addition to the above requirements for confinement of concrete, NZS 3101: 1995 has additional requirements for transverse reinforcement to prevent premature buckling of longitudinal reinforcement (which will govern when axial loads on columns are small) and for transverse reinforcement to prevent shear failure. The designer provides transverse reinforcement for the most critical of these three requirements. It is important that designers calculate the design axial loads at the ultimate limit state correctly using capacity design. If the axial column loads are underestimated (as they may be if they are calculated for the code forces using elastic theory) the column flexural strength may be overestimated and the confined lengths of column may be underestimated. The design axial loads in the columns of a weak-beam-strong-column frame should be derived from the shear forces applied at the column faces by the gravity loads from the beams and the moment induced shears from the beam plastic hinge moments in both directions acting at flexural overstrength. A reduction in the moment induced shears can be allowed, to take into account the probability that not all beam plastic hinges have reached their overstrength simultaneously up the height of the frame. NZS 310 1: 1995 gives a procedure for this calculation.

Seismic Tests of Precast Beam-to-Column Joint Subassemblages With Unbonded Tendons

Two ungrouted post-tensioned, precast concrete beam-to-column joint subassemblages were tested under cyclic reversals of inelastic displacement to determine seismic response. One subassemblage represented an exterior joint while the other was an interior joint of a one-way prestressed concrete frame. The large scale test units were designed with greatly reduced beam and joint shear reinforcement compared with equivalent monolithic joints, but with special spiral confinement of the beam plastic hinge regions. Both subassemblages performed well, with only minor, cosmetic damage being recorded up to drift ratios of 3 percent or more. Energy absorption of the hysteretic response, though small, was larger than expected and residual displacements were negligible. It is concluded that satisfactory seismic performance can be expected from well-designed ungrouted precast, post-tensioned concrete frames.