Ductile Frames Research Articles

Design procedure of a shear fuse system for steel moment-resisting frames

In steel moment-resisting frames (MRFs), seismic energy is generally dissipated through the formation of flexural plastic hinges at beam ends. In ensuring such a mechanism, current code provisions limit the utilization of beams with small span-to-length ratios in MRFs. This study presents the design procedure of a novel shear fuse system that integrates replaceable shear links with non-prismatic beams to enhance the performance and repairability of MRFs with small beam span-to-length ratios. The proposed design strategically weakens the beam at its midspan by incorporating a replaceable link, prioritizing shear yielding in the link over flexural yielding in the beam outside the link, thus ensuring adequate frame ductility and protecting the critical beam-to-column connections. It can function as an efficient replaceable shear fuse system, as the damaged fuse can be substituted with a new one following a severe earthquake. In fulfilling the study’s purpose, first, several formulas are developed to provide a comprehensive design procedure. Next, example design calculations are presented for an MRF with a small beam span-to-depth ratio. Ultimately, a numerical investigation is provided to examine the proposed system’s performance compared to conventional MRFs. The results indicate that the proposed shear fuse system provides a more consistent cyclic behavior than the conventional prismatic beam design, exhibiting stable strain-hardening behavior up to the 5 % story drift ratio without noticeable strength degradation. It appropriately shifts the plastic hinges away from the beam-to-column connections while increasing the frame’s overall ductility with 1.14 times greater energy dissipation in the final loading cycles.

Seismic performance of two-story three-bay reinforced concrete frame equipped with K-configured buckling restrained braces

This study presented experimental and numerical investigations into the seismic performance of reinforced concrete (RC) frames equipped with buckling restrained brace (BRB) systems in the central span. The study evaluated the effectiveness of the K-configured BRB system in strengthening the RC frame for engineering construction applications in the seismic region. A 1/3-scaled, three-span, two-story, RC frame was designed in accordance with seismic design requirements and tested under low-reversed lateral cyclic loading. A finite element model of the BRB-equipped RC frame was created using ABAQUS and validated by comparing the numerical and experimental results. The validated model was also modified by removing the BRBs to create the bare RC frame. Seismic behaviors of the bare and RBR-equipped RC frames were numerically examined and compared in terms of failure modes, hysteretic response, ductility, energy dissipation, strength degradation, and stiffness deterioration. The results indicated that the BRB-equipped RC frame achieved a plastic hinge failure mechanism at the beam ends with no severe concrete damage in the supporting columns. Furthermore, the use of the K-shaped BRB in the central span improved the load-carrying capacity by up to 80% and the energy dissipation capacity by up to 50%. Parametric studies were also conducted to investigate the influence of critical design parameters and provide design suggestions for potential improvement in the RC frame's ductility and energy dissipation capacity.

Influence of the Dead Loads in the Seismic Design of Ductile Frames of Reinforced Concrete

This paper evaluate the influence of the dead load reduction in the seismic design of a public building to be built at the zone of bigger seismic hazard of Cuba on a soil type D by Cuban seismic code NC 46:2017. The evaluation was carried out by comparing the structural design of a heavy and a lightened variant, based on the design of the critical sections of the superstructure including the joints. The seismic solicitations by static equivalent method are offered by computers program SAP 2000NL version and combined with gravitational loads by actual Cuban code. The structural design was carried out by the limit resistant capacity method, using the Excel Workbook DISRESPLAS and consulting the design formulations in international reference standards. Finally, it is shown that a moderate reduction of dead load significantly rationalizes the structural design and simplifies the construction details, in particular, the joints.

Nonlinear Static Response of Low-Moderate Ductile Chevron Concentrically Braced Frames Designed According to Eurocode 8

Steel frames equipped with chevron bracing (Λ-CBF) are usually less ductile than other steel systems. Therefore, in many cases, it can be convenient to design Λ-CBF to exploit their stiffness and resistance to enforce a pseudo-elastic seismic response of the building in low to moderate seismic zones. In current EC8, the rules for moderate Λ-CBF are the same as those for high ductile frames, thus potentially leading to massive, over-resistant and uneconomic systems. In the next version of EC8 new rules have been set to design moderate ductile Λ-CBF, aiming to enhance the ease of use of the code as well as to obtain less expensive structures. The new rules of the updated EC8 are based on local requirements and elastic calculation without any plastic analysis. This paper discusses these rules that are numerically investigated by means of nonlinear static analyses on a set of 8-storey steel frames designed for different seismic intensities. The performed analyses show that the frames designed according to the updated EC8 exhibit moderate ductility, preventing damage to brace-intercepted beams and reducing ductility demand on braces under compression.

Finite Element Analysis of Frames with Reinforced Concrete Encased Steel Composite Columns

Structural frame systems that consists of concrete-encased-steel-embedded composite columns and reinforced concrete beams are typically used in mid-rise to tall buildings. In order to understand their overall structural behavior, a total of 12 frame models with high and low ductility features were constructed and analyzed using LS-DYNA software. Two of these models were validated using the results of previously tested frames. The remaining 10 models were studied to predict the behavior of frames with varying concrete strengths, reinforcement configurations, and structural steel sections under vertical and lateral loads. The results were investigated in terms of cracks and failure patterns, load-deflection relationships, energy dissipation, and stiffness degradation. The analytical results indicated that the high ductile frame models showed slightly better lateral load carrying performances compared to low ductility frame models. Moreover, the analytical studies demonstrated that the existence of structural steel in a column, regardless of its cross-sectional shape, was the most important parameter in improving the lateral load carrying capacity of a frame.

System reliability assessment of ductile frame structures using methods of moment

Reliability assessment of ductile frame structures in a systematic manner has remained a challenging issue because of the difficulties in searching for important failure modes and evaluating the system probability of failure stemmed from these important modes. In this paper, based on the Box-Cox transformation, a new failure mode independent performance function with the probability distribution of weak non-normality is proposed for the system reliability assessment of ductile frame structures. An efficient approach is then developed for estimating the failure probability of the proposed performance function, which includes two steps: first, the point-estimate method based on hybrid dimension-reduction integrated with structural limit analysis is developed to evaluate the first four central moments (i.e., mean, standard deviation, skewness, and kurtosis) of the proposed performance function; next, the system probability of failure corresponding to the proposed performance function is then estimated using the moment-based reliability method. Three numerical examples are presented to demonstrate the efficiency and accuracy of the proposed method, where the method of subset simulation is employed for comparison. It can be concluded that the developed methodology successfully overcomes the two difficulties including the identification of important failure modes and the evaluation of system probability of failure stemmed from these important modes in system reliability assessment of ductile frame structures.

Strengthening of Infilled Wall with RC Framed Structure Under Provision of Single Equivalent Diagonal Strut Action

Infilled wall in R.C framed systems one of the essential contribution of non-structural detail. Normally infilled wall usually does now not take any load and it isn't don't forget in design a part of R.C framed systems. The essential purpose of this study to perceive the interaction amongst R.C.Body with infilled wall. In this experimental study, three specimens may be prepared one-10th scale version below the subsequent methodologies, R.C.Framed form without infill, R.C.Framed shape with reinforcement along the brick masonry, R.C.Framed structure with reinforcing band under damper conditions. A series of experiments have been performed on one-8th-scale model of the framed systems. This look at discusses the aspect of strength, ductility and failure mechanism of the frame under static loading. The test stop result shows that the final load carrying functionality of R.C.Frame with reinforcement band is 1.472 instances more than that of R.C.Frame with out infill. The preliminary stiffness of the body with diagonal strut is 1.0.Five times higher than that of the frame with out infill. The ductility of frame with reinforcement band is 1.137 instances extra than that of frame without infill. The preliminary stiffness of the frame with reinforced brick masonry is greater than that of frame with out brick masonry. The ductility of body with reinforcement band is 1.137 instances greater than that of body with out infill. Comparing the failure sample with reinforcement band is avoid the surprising falling due to bedding joint failure. The diagonal strut beautify the strength at joints and it reduces the diagonal cracking failure.

Seismic damage state predictions of reinforced concrete structures using stacked long short-term memory neural networks

Early and accurate damage evaluation after earthquakes is critical for planning an efficient and timely emergency response. State-of-the-art rapid evaluation techniques of structural damage include the use of fragility or vulnerability curves. However, fragility-based damage functions may vary significantly, depending on the ground motion characteristics, soil conditions, and structural geometric properties. A novel stacked long short-term memory (LSTM) network with overlapping data was developed in this study to overcome this issue. The ground motion time histories are divided into several stacks and feed to the LSTM network, and the data are overlapped with the preceding stack to link each stack. The stacked LSTM reduces the temporal dimension by stacking and generating new features, and shortens the time required for training. The proposed network significantly reduces the training time required (approximately 97%) and enhances the test accuracies (80%–95%) as the number of stacks increases. OpenSees is utilized for the creation of the numerical model of ductile frames (using concentrated plasticity modeling approach) and nonductile frames (using distributed plasticity modeling approach). Although these structures have different response mechanisms, the proposed LSTM network shows the diversity in predicting the earthquake-induced damage with a high degree of accuracy (80%–95%). The performance of the proposed model on different types of structures (nonductile and ductile building frames and a non-ductile bridge) with the same network shows the flexibility of the model.

Seismic performance of exterior beam-column joints constructed with engineered cementitious composite: Comparison with ordinary and steel fibre reinforced concrete

Joint and plastic hinge regions of a ductile frame structure must be carefully detailed to ensure that the required ductility could be provided as intended, particularly when a high level of ductility is aimed for. However, the stringent detailing requirements for ductility often result in densely spaced transverse reinforcement which adds to construction difficulties. This paper presents an attempt to relax some requirements in transverse reinforcement spacing in the joint and potential plastic hinges of ductile moment-resisting frame structures using a damage-tolerant concrete known as the engineered cementitious composite (ECC). Results of reversed cyclic loading tests on two ECC beam-column joints are presented and compared with the response of companion specimens constructed with ordinary and steel fibre reinforced concretes (SFRC). Detailed documentation of key seismically important features is presented, along with a series of digital crack maps to provide a fuller understanding of the evolution and extent of damage under loading. It is shown that the seismic performance of the ECC specimens with relaxed detailing was similar and, in some cases, better than the companion concrete specimen which was designed in accordance with seismic design provisions. The ECC specimens displayed a considerably thicker hysteresis response with less pinching and smaller residual drifts, whereas the SFRC specimen retained a similar overall profile of the concrete joint. Throughout the testing, it was found the joint in the ECC specimens remained intact, while that in the concrete specimens displayed severe cracking under large displacement reversals.

Cyclic loading test and nonlinear analysis on composite frame consisting of steel reinforced recycled concrete columns and steel beams

A two-span and three-story of the frame specimen with a scale of 1:2.5 was tested and investigated under cyclic loading to study the seismic behavior on the composite frame consisting of steel reinforced recycled concrete columns and steel beams. After observing the loading process and failure modes, the mechanical properties of composite frame, such as the load–displacement hysteretic curves, skeleton curves, bearing capacity, interstory displacement angles, ductility, energy dissipation and stiffness degradation, were analysed in detail. On this basis, a finite element model of the composite frame which considered the constitutive properties of recycled concrete was established. The deformation diagram, stress nephogram and calculated skeleton curves of composite frame were obtained, and a nonlinear parameter analysis was also conducted. The experimental and numerical analysis results all show that the plastic hinges appeared at the end of steel beams firstly and then formed at the end of columns, which is a typical plastic hinge failure of frame. The hysteretic curves of frame are shuttle-shaped and full, and the descending section of the skeleton curves and stiffness degradation curves is relatively gentle. The average ductility coefficient, equivalent viscous damping coefficient and ultimate interstory displacement angle of frame are 3.205, 0.303 and 0.04, respectively. Therefore, the composite frame has good deformation, energy dissipation capacity and collapse resistance. The results of the nonlinear parameter analysis on the frame also exhibit that increasing the strength of steel products or recycled concrete is beneficial to the horizontal bearing capacity and lateral stiffness of frame. The maximum increase in the bearing capacity of frame can be 21.5% when the profile steel strength is increased from Q235 to Q390 and the recycled concrete strength is maintained at C40 within the parameters analysed, but the increase in material strength is unfavourable to the deformation capacity of frame. Increasing the axial compression ratio of columns in the frame obviously weakens the lateral displacement ductility of frame, which makes the frame unsafe under an earthquake. In addition, the bearing capacity and stiffness of frame increases with the increase in the linear stiffness of beams and columns. The research conclusions can provide a reference for the engineering application of this type of composite frame.

Seismic behavior of plane frame with special-shaped CFST columns, H-shaped steel beams and vertical rib connections

The seismic behavior of special-shaped concrete-filled steel tubular (CFST) column to H-shaped steel beam plane frame (SCFSTF) with vertical rib connections was investigated experimentally and numerically in this study. Double-bay two-story SCFSTFs with the scale ratio of 1/2 were tested under constant vertical compressive load and cyclic horizontal loads (or displacements), which is a pseudo static experiment considering the axial load ratio. Based on the experimental results, failure modes, bearing capacity, hysteretic curve, skeleton curve, energy dissipation, ductility, rigidity degradation and strength degradation of SCFSTFs were investigated. As a result, a typical strong column-weak beam failure mode was determined. The degradation in strength and rigidity were minimal and energy dissipation capacity and ductility of frames were adequate, demonstrating excellent seismic performance. Besides, energy dissipation capacity and horizontal resistance were improved with axial load ratio increasing within the parametric range of this test. After the test, a finite element method based on software ABAQUS was carried out to further investigate the seismic performance. The numerical results of skeleton curve, rigidity, yield load, peak load and stress distribution agreed well with the test results. The plastic hinge formation process and ultimate failure mode were further investigated using the finite element model.

Experimental Study on Seismic Behavior of RC Frame Beam Column Joints

Strong columns and weak beams and "strong joints and weak members" are important concepts in the design of reinforced concrete ductile frame structures. However, many earthquake damages show that a large number of reinforced concrete frame structures still do not guarantee the realization of the above seismic concepts. In order to solve this problem, this paper designs and manufactures a beam column joint with plate, which includes the bottom column base and the moment increasing coefficient of the column end is 1.2. Through the quasi-static reciprocating loading test, the influence of the bearing capacity, ultimate deformation, stiffness degradation and hysteretic energy consumption of the specimen is investigated. The test results show that when the moment increasing factor at the end of the column is 1.2, the failure order of the specimen is bottom column base beam slab bottom column base, the plastic hinge occurs at the bottom of the column, and the position of the column in the beam column joint is not damaged; According to the seismic code, the overall failure mode of the beam column joints with slab and infilled wall at the bottom column base can be "strong column and weak beam" and "strong joint and weak member" under the action of reciprocating quasi-static loading.

Experimental study on seismic behavior of concrete filled square tubular frame with staggered beam-to-column joints

To investigate the seismic behavior of concrete-filled square tubular frame with staggered beam-to-column joints, A CFST frame with staggered beam-to-column joints and a CFST frame with conventionaljoints were tested undercyclic loading. The hysteretic behavior, frame ductility, degradation of stiffness and strength, and failure mechanism were analyzed. The two test frames exhibited beam hinge failure mechanism, the hysteretic loops of the frames were spindle-shaped, the strength and stiffness decreased gradually, and the ductility coefficient and energy dissipation ratios met the requirements for seismic design of ductility frame. CFST frame with staggered beam-to-column joints exhibited weaker hysteresis behavior, maximum load, damage displacement and energy dissipation capacity compare to CFST frame with conventional joints. Analysis of the mechanical mechanism of joints revealed that the interior joint form has a important influence on the seismic behavior and failure mechanism of the frame. The research results provide reference for the seismic design of CFST frame structures with staggered beam-to-column joints.

Effect of corrosion in reinforced concrete frame components on pushover behavior and ductility of frame

AbstractChloride‐induced corrosion of reinforced concrete (RC) is one of the main reasons for decreasing the seismic performance level of RC structures over their lifetime. In the present study, base shear capacity and ductility were considered as criteria for evaluating seismic performance of the RC frame. The impact of corrosion on the ductility and base shear capacity of a two‐dimensional single‐story single‐span RC frame was investigated using nonlinear static analysis considering the deterioration of the mechanical properties of the rebar and concrete. The corrosion damage model was implemented using fiber sections and nonlinear elements, and then pushover analysis over 0, 15, 30, 45, and 60 years of life was performed. The strain penetration effect was considered in the fiber model at the column‐footing joints. The accuracy of modeling was validated with experimental data of the RC frame subject to cycle loading. The final results showed that by decreasing the water‐to‐cement ratio and increasing the cover thickness, the seismic performance of the RC frame is preserved over a lifetime. The time‐dependent ductility of the RC frame was evaluated at two structural and cross‐sectional levels. The results revealed that the corroded RC frame has a lower base shear capacity, ultimate drift, and ductility than the intact RC frame. Also, the corrosion‐induced deterioration of rebar and concrete significantly decreases the seismic performance of the corroded RC frame.

Numerical Evaluation of Dynamic Responses of Steel Frame Structures with Different Types of Haunch Connection Under Blast Load

This research is aimed at investigating the dynamic behaviour of, and to analyse the dynamic response and dynamic performance of steel frames strengthened with welded haunches subjected to a typical hydrocarbon blast loading. The structural dynamic analysis was carried out incorporating the selected blast load, the validated 3D model of the structures with different welded haunch configurations, steel dynamic material properties, and non-linear dynamic analysis of multiple degree of freedom (MDOF) structural systems. The dynamic responses and effectiveness of the reinforced connections were examined using ABAQUS finite element software. Results showed that the presence of the welded haunch reinforcement decreased the maximum frame ductility ratio. Based on the evaluation of the results, the haunch reinforcements strengthened the selected steel frame and improved the dynamic performance compared to the frame with unreinforced connections under blast loading, and the biggest haunch configuration is the “best” type.

Shake table investigations on code non-compliant reinforced concrete frames

Shake-table tests were performed on a code conforming and four non-compliant 1:3 reduced scale two-story RC frames. The models were subjected to 1994 Northridge earthquake acceleration time history, linearly scaled to multiple levels for studying the progressive damages. The code conforming model was observed with plastic hinges at the beam-ends and base of columns on ground story. This frame incurred only slight cracks in the joint panels under extreme shaking. The code-conforming model resisted input excitation with peak horizontal acceleration of 1.0 g before attaining the incipient collapse state. The non-compliant models were observed with plastic hinges in beam/column members, and incurred extensive damages in beam-column joints under extreme shaking. The fully non-compliant frame resisted peak horizontal acceleration of 0.50 g before attaining the incipient collapse state. The response modification factor of code-conforming model is 7.54 that reduced to 2.90 in case of fully non-compliant frame, which was due to the non-compliance of constructions. This was partly due to the reduction in the overstrength of frame (which was about 20%) and partly due to the reduction in ductility of frame (which was about 50%), in comparison to the seismic response parameters given in the seismic code. The less redundant structural system and joint shear hinging are the main reasons resulting in the reduction of overstrength and ductility, respectively. Static force based performance assessment in various seismic zones revealed that the code-conforming frame performance is “OK” while non-complaint frames performance is “NG” in both seismic zone 3 and zone 4. The present research suggests a reliability/redundancy factor to take in to account in proposing response modification factor for seismic design of structure. This will take care of the construction deficiencies found in the region. This factor can vary from 1.0 (in case of fully compliant structure) to 0.40 (in case of fully non-compliant structure).

Near fault ground motion effects on seismic resilience of frame structures damaged in Wenchuan earthquake

This paper reports the study of the effects on structural seismic resilience of near fault pulse-like ground motions recorded in the 2008 Wenchuan earthquake. Some near fault pulse-like and far fault nonpulse-like ground motions recorded in the Wenchuan earthquake were selected as excitations for nonlinear dynamic analysis. A low-ductile reinforced concrete frame and a modern ductile frame were considered to compare seismic resilience of frames constructed before and after the Wenchuan earthquake. The building-based loss evaluation approach in HAZUS was modified to explicitly consider the effect of residual story drifts, which provides an accurate loss evaluation method and still retains simplicity. Fragility curves were derived from incremental dynamic analysis. Loss vulnerability curves for frames were obtained based on the proposed method. Functionality restoration curves and resilience index were then estimated. The results show that the Wenchuan near fault pulse-like ground motions can induce higher collapse and demolition risks for frames. Total losses of frames are higher under pulse-like ground motions, and the resilience of frames is reduced. Ignoring residual story drifts will underestimate total losses, especially for frames under pulse-like ground motions. Finally, the modern ductile frame shows enhanced earthquake resilience compared with the low-ductile frame.

Cyclic Performance and Mechanical Characteristics of the Oval-shaped Damper

Every year earthquake damage causes hundreds of death all over the world. As much as possible, buildings should be kept in the elastic zone during an earthquake, therefore, the failure of building the main member is reduced. This paper investigated an oval steel shaped yielding damper used for seismic protection of chevron steel braced frames. The damper is designed to deform in-elastically under shear deformation to become energy dissipated. This oval steel shaped damper improves the braces buckling problem and reduces the required area cross section of chevron steel bracing members. To do this, eight models of the damper are proposed. For this purpose, finite element (FE) analysis with ABAQUS software is used to investigate and model the oval-shaped damper (OSD). The present study also investigated the damper strength parameters and seismic performance for applying to the steel braces frame. It is shown that the damper added between the chevron braces and the upper beam can reduce the lateral displacement and base frame force. Hence, the oval steel shaped damper is capable to absorb a great amount of energy with a stable hysteresis behavior. To do this, relationships are proposed and developed based on the maximum capability of the damper. The results show that this damper is responsible for absorbing input energy and increasing ductility frame coefficient. By comparing the analytical method and theoretical results, it is calculated that the proposed equations can be adapted to calculate seismic parameters like ultimate stress, ultimate shear force, plastic moment, elastic stiffness, stiffness degradation, deformation capacity, and resistance of the damper and calculate the exact location of plastic hinge. The structural designer, researchers and someone who like to develop the researches, it can be used and benefit for structural engineering.

A Simple Approach for the Design of Ductile Earthquake-Resisting Frame Structures Counting for P-Delta Effect

In the last decades, the possibility to use the inelastic capacities of structures have driven the seismic design philosophy to conceive structures with ductile elements, able to obtain large deformations without compromising structural safety. In particular, the utilization of high-strength elements combined with the purpose of reducing inertial masses of the construction has highlighted the second-order effect as a result of the “lightweight” structure’s flexibility. Computational aspects of inclusion of the second-order effects in the structural analysis remain an open issue and the most common method in the current design practices uses the stability coefficient θ. The stability coefficient estimates the ratio between the second-order effect and lateral loads’ effects. This coefficient is used then to amplify the lateral loads’ effects in order to consider the second-order effects, within a certain range proposed by codes of practices. In the present paper, we propose a simple approach, as an alternative to the stability coefficient method, in order to take into consideration P-Delta effects for earthquake-resisting ductile frame structures in the design process. The expected plastic deformations, which can be assessed by the behavior factor and the elastic deformations of the structure, are expected to magnify the P-Delta effects compared to those estimated from an elastic approach. The real internal forces are approximated by modifying the stiffness matrix of the structure in such a way as to provide a compatible amplification effect. This concept is herein implemented with a three-step procedure and illustrated with well-documented case studies from the current literature. The obtained results show that the method, although simple, provides a good approximation compared to more refined and computationally expensive methods. The proposed method seems promising for facilitating the design computations and increasing the accuracy of the internal forces considering the second-order effects and the amplification from the inelastic deformations.

A simplified retrofitting method based on seismic damage of a SDOF system equivalent to a damped braced building

A new Displacement-Based Design (DBD) procedure to proportion hysteretic damped braces (HYDBs) is proposed in order to take into account the effects of the seismic degradation of a structure that needs to be retrofitted. To this end, a hysteretic model based on plastic and damage mechanisms is adopted to describe the inelastic response of reinforced concrete (r.c.) frame members. Then, nonlinear seismic analysis of a single-degree-of-freedom system, equivalent to a multi-degree-of-freedom model of the structure, is used to generate the capacity boundary curve by means of the hysteretic model defined starting from the initial backbone curve. Two-, four- and eight-storey r.c. framed structures are designed for a medium-risk seismic zone of a former Italian code. These are then to be retrofitted by inserting HYDBs to attain performance levels imposed by current Italian code in a high-risk seismic zone. Different retrofitting solutions are compared, considering for each retrofitted structure: (i) variable damper ductility coupled with constant frame ductility; (ii) variable frame ductility coupled with constant damper ductility. The effects of different damage levels and different damage evolution laws are also investigated. Finally, pushover curves of the unbraced and damped braced structures are carried out, with and without considering degradation of the hysteretic response of r.c. frame members on the DBD procedure of the HYDBs.