Concrete Moment Resisting Frame Structures Research Articles

Comparative Analysis of the Impact of Vertical Irregularities on Reinforced Concrete Moment-Resisting Frame Structures According to Eurocode 8

Comparative Analysis of the Impact of Vertical Irregularities on Reinforced Concrete Moment-Resisting Frame Structures According to Eurocode 8

Corrosion effects on the dissipative performance of critical regions of RC frame systems

The influence of degradation phenomena on the dissipative performance of critical regions of reinforced concrete moment-resisting frame structures is investigated through the execution of in-depth numerical analyses reproducing corrosion effects. The model proposed by the Authors in a previous research paper, calibrated using the results of a wide experimental campaign on real-scale substructures, is used for simulating the seismic/cyclic behaviour of plastic hinge regions in correspondence of beam-to-column joints and base-column joints, considering different typologies of reinforcing bars. Corrosion effects were considered in terms of degradation of the mechanical properties of materials (both rebars – longitudinal and transversal, and concrete), confinement deterioration and modification of the bond-stress law as function of the corrosion entity. Results are presented comparing the reference with the different corroded conditions, providing a rational and consistent analysis of corrosion effects in terms of damage, modification of failure modality, material and bond/slip performance.

Comparison of seismic fragility of RC moment-resisting frame structures designed according to Chinese and Indian code

Seismic fragility analysis is a method used to evaluate the vulnerability experienced by structures when subjected to earthquakes. In this study, the seismic performance of 18 reinforced concrete moment-resisting frame structures designed according to Chinese code and Indian code is analyzed. A parametric study is conducted by varying the height of the building and the type of soil on which the building is constructed. Nonlinear time history analyses are conducted to develop fragility curves for four different damage levels: fully operational, operational, repairable, and collapse prevention. Linear regression analysis is conducted to correlate the engineering demand parameter (maximum inter-story drift) and the intensity of an earthquake (peak ground acceleration). The results show that the structures designed according to the Indian code experience higher story drift than those designed according to Chinese code, making them more vulnerable to the same earthquake intensity.

Influence of nano-silica in beam-column joint flextural properties

The performance of reinforced concrete moment resisting frame structures in present-day earthquakes across world has highlighted the outcome of poor performance of beam-column junction, usually important in the reinforced concrete frame design. In reinforced concrete moment resisting frame the beam column joints are crucial zones for load transfer productively between the linking elements (i.e. beams & columns) in the structural design. So this is especially necessary to reduce the vulnerability of Beam-Column joint in connection with the Seismic loading. In this investigational examination, Fly ash, a throw away product, generated in thermal power stations is roughly around 105 million tons every year (in India) whose percentage usage is less than 13%, was added. This reduction in strength was tried to compensate by adding 0 to 2.5% of Nano Silica (nS) as it reacts with calcium hydroxide (Ca(OH)2) mini crystals, and are array in the Interfacial Transition Zone (ITZ) linking hardened cement paste and aggregates, evenly produce C–S–H gel. Nano-SiO2 can also behave as nucleus to tightly bonded elements with cement hydrates. Fly ash concrete with respect to nano-SiO2 maintains higher density and strength. High-strength concrete with respect to nS owns higher flexural strength. On an average 7 exterior Reinforced Concrete beam-column joint specimens (control) were casted, cured for complete 28 days and tested to failure. Only three contained Fly ash (20%, 40% and 60%) and the other three specimens with nS (2.5%) and Fly ash (20%, 40% and 60%). Evenly, on the column an axial load was applied. Then seismic load (i.e. Push and pull load) was applied at the free end of the cantilever beam till failure occurs. The reinforced Nano concrete Beam-Column joints and the Fly ash mixed RC Beam-Column joints were compared each other and the test results are obtained.

Displacement profile for displacement based seismic design of concentric braced frames

The direct displacement based design (DDBD) procedure is well developed and used for designing reinforced concrete and steel moment resisting frame structures, wall structures and bridges. However, a limited number of studies is available on designing steel concentric braced frame (CBF) structures using DDBD approach. Moreover, those studies use the design displacement profile proposed for the reinforced concrete moment resisting frame structures by Priestley et al. (2007). Furthermore, Wijesundara et al. (2018) have highlighted that higher interstorey drifts can be observed in CBFs during the inelastic response due to the effects of higher mode amplifications. Therefore, the main objective of this study is to propose a new design displacement profile that is capable of predicting the effects of higher mode amplifications on the displacement profile for designing steel CBFs.In this regard, an attempt is made to develop a design displacement profile based on the median maximum storey displacements obtained from the nonlinear time-history analysis for a set of real ground accelerations. For this purpose, twelve different steel CBF structures with varying brace configuration, braces slenderness over the height of building, and different heights are selected. Nonlinear timehistory analyses are performed for the 3-D nonlinear finite element models of the selected frames using OpenSEES software. The developed models are capable of simulating the out-of-plane buckling. The models are subjected to a set of 30 real ground motion records with varying levels of spectral acceleration at the first modal period of the structures. The maximum storey displacement at each storey levels is recorded for all the ground motion records. On the basis of the observed storey displacement and interstorey drift, the appropriate design displacement profile for CBFs is proposed. The proposed equations show a high correlation with the observed behaviour of the suggested CBFs.

A vector intensity measure to reliably predict maximum drift in low- to mid-rise buildings

An optimal intensity measure (IM) should be able to predict the structural response with minimum dispersion, which is called efficiency, and also independently of other ground motion characteristics, such as earthquake magnitude (M) and source-to-site distance (R), which is called sufficiency. Using an optimal IM can play an important role in reliable seismic performance assessment of structures. The present study is aimed at investigating the efficiency and sufficiency of vector-valued IMs for predicting maximum inter-storey drift ratio (MIDR). The IMs considered in this study include response spectral acceleration at the fundamental period of the structure, Sa(T1), as a common scalar IM, the vectors (Sa(T1), εSa) and (Sa(T1), NP) as well-known vector-valued IMs, and ten other vector-valued IMs. These ten IMs consist of two components, with Sa(T1) as the first component and different parameters that are ratios of scalar IMs as the second component. By investigating the desirable features of an optimal IM, (Sa(T1), Sa(T1)/PGV) is proposed as an optimal vector-valued IM for the prediction of MIDR demand on low- to mid-rise reinforced concrete moment-resisting frame structures. To make the proposed IM predictable, a ground motion prediction equation (GMPE) is determined for Sa(T1)/PGV by using the existing GMPEs.

Numerical Modelling of Seismic Behavior of Retrofitted RC Beam-Column Joints

In the event of an earthquake, the beam-column joints in the reinforced concrete moment-resisting frame structures are affected by a high level of deformations and stresses. Due to these deformations and stresses, the joint can be damaged and even fractured in some cases. The failure of the beam-column joint can cause the building to collapse. In recent years, particular attention has been paid to strengthening joints in the substandard RC buildings. In this paper, the beam-column joint is investigated considering the nonlinear behavior for concrete and steel. For concrete, the damage plasticity model and for reinforcing steels bilinear plasticity model is used. Several examples of tested joints in the technical literature have been modeled before and after strengthening, then numerical and experimental results are compared. Seismic performance of joints has also been studied. The results of this research show good agreement between the results of finite element model and experimental results. Moreover, the retrofitting method have shown could improves the seismic performance of the joint.

Risk Analysis of Three-storey Reinforced Concrete Moment-resisting Frame Structures Using Performance-based Wind Engineering

This paper discusses the application of concepts of performance-based wind engineering used to determine the effects of changing building design elements to the performance of a structure against severe wind hazards in the Greater Metro Manila Area, Philippines. Only three-storey reinforced concrete moment-resisting frame structures were subject to analysis through computational fluid dynamics. Before assessing the performance of structures, severe wind hazards for the study area was characterized by collecting wind speed data from over 50 years and fitting the data using the Gumbel distribution. The building stock was developed by varying roof pitch and floor aspect ratio values in certain set increments. Roof pitches observed were 15, 30, and 45 along with structures with floor aspect ratios of 1:1, 1:2, and 1:3. The damage to roof and windows, as well as the damage index which gives the ratio of the repair cost to the replacement cost of a building, were identified. Damage for each model was classified according to the Hazard-US Damage State Matrix in order to generate a damage probability matrix. From this damage probability matrix, the probability of exceedance of each damage state was compute by taking the cumulative probabilities. Data points for each damage state were then fitted with a lognormal function. Vulnerability curves were developed by multiplying the probability of exceedance of each damage state to cost percentages adopted from the UPD-ICE Report [2]. Damage indices were computed per wind speed by summing the total damage for damage states. Wind speed versus risk density curves were generated by multiplying values for each data point in the vulnerability curves to the probability density function of the hazard. Risk curves were then obtained by plotting wind speeds against values of damage indices that correspond to said wind speeds. One key observation is that damage percentage increased as roof pitch also increased, having as much as around a 15% difference between structures with roof pitches of 15 and 45. Slender structures whose windward sides were also the long sides had the most damage. For all structures, a top-to-bottom progressive damage trend was observed.

Strut-and-tie modelling for the analysis and design of RC beam-column joints

Beam-column joints have been recognised as one of the potentially weaker elements of reinforced concrete moment-resisting frame structures when subjected to seismic lateral loading. Prior earthquake reconnoitring reported the notable damage that can develop from inappropriate beam-column joint design. Design formulae available in building codes and literature differ considerably in functional form, do not consider all of the key variables that affect the joint response, and broadly predict quite different values of shear strength from one another. A mathematical model based on the strut-and-tie model is developed to estimate the shear strength of exterior and interior reinforced concrete beam-column joints. The proposed model leads to an explicit single closed-form expression for computing the shear strength and accounts for the shear stress contributions provided by the diagonal concrete strut and the shear reinforcement (including both joint hoops and column intermediate bars), while considering those variables that significantly affect the behaviour of such joints. Model parameters were calibrated using the experimental results of 454 exterior and interior joints available in the literature. When compared to a number of predictive expressions for the shear strength of joints, the proposed model provides the best fit with the measured shear strength. Further, a set of simple code-oriented design formulae, with conservative predictions, is proposed to facilitate practical engineering design.

Energy Absorption Capacity of Reinforced Concrete Beam-Column Connections, with Ductility Classes Low

Once the behaviour of reinforced concrete moment resisting frame structures is investigated, it is concluded that the performance of beam column connections is not satisfactory. In order to understand the complex mechanisms and satisfactory behaviour of beam column connections, lots of investigations have been done. The most critical zone in reinforced concrete moment resisting frames would be the beam column connection. The behaviour of beam column connection once it is subjected to large forces during earthquakes has a great impact on the response of the structure. The shear failure has a brittle nature which is not a desirable structural performance during earthquakes. Two new types of shear reinforcements design are introduced in this study for the purpose of reaching a higher performance and material capacity for the connection and hence, the structure. These two shear reinforcement designs working simultaneously with other reinforcement systems and concrete have a better performance compared to that of conventional methods. The first specimen is made according to conventional method of design as control specimens in conformance with Euro code EC2 & EC8. The second specimen introduces a continued shear resistance system against discontinued conventional shear resistance system (stirrups) which is called “Single Square Spring Shear Resistance System” (SSSSRS). The third specimen possesses two continued square spring systems twisting together and making a parallel system called “Double Square Spring Shear Resistance System” (DSSSRS). A comparison was made between the performances of the improved shear reinforcement systems of beam-column connections against the control specimens. It was concluded that a lower deflection along with higher energy absorption was achieved for “Single Square Spring Shear Resistance System” (SSSSRS) and “Double Square Spring Shear Resistance System” (DSSSRS) compared to control specimens.

Direct displacement-based seismic design of steel concentric braced frame structures

The direct displacement-based design (DDBD) procedure is well developed and used for designing reinforced concrete moment resisting frame structures, wall structures and bridges. However, there is limited number of studies available on designing steel concentric braced frame (CBF) structures using DDBD approach. Therefore, it is necessary to develop a DDBD procedure for CBF structures. On this regards, this paper proposes a DDBD procedure for steel CBF structures. The proposed procedure utilises the yield displacement shape derived on the basis of tensile yielding of the braces, and the equivalent viscous damping equation of the system proposed by Wijesundara et al (2011) as a function of system ductility and non-dimensional slenderness ratio for steel CBF structures. Finally, the performance of four steel CBF structures designed according to the proposed DDBD procedure is studied using non-linear dynamic response of the structures. The results show that the performance of CBF structures is in good agreement with the design considerations.

Direct Displacement-Based Seismic Design of Steel Concentric Braced Frame Structures

The direct displacement-based design (DDBD) procedure is well developed and used for designing reinforced concrete moment resisting frame structures, wall structures and bridges. However, there is limited number of studies available on designing steel concentric braced frame (CBF) structures using DDBD approach. Therefore, it is necessary to develop a DDBD procedure for CBF structures. On this regards, this paper proposes a DDBD procedure for steel CBF structures. The proposed procedure utilises the yield displacement shape derived on the basis of tensile yielding of the braces, and the equivalent viscous damping equation of the system proposed by Wijesundara et al (2011) as a function of system ductility and non-dimensional slenderness ratio for steel CBF structures. Finally, the performance of four steel CBF structures designed according to the proposed DDBD procedure is studied using non-linear dynamic response of the structures. The results show that the performance of CBF structures is in good agreement with the design considerations.

Finite element model updating of a semi-rigid moment resisting structure

Partial-strength composite steel–concrete moment-resisting frame structures can be designed to develop a ductile response in components of beam-to-column joints and column bases, including flexural yielding of beam end plates, shear yielding of column web panel zones and yielding of anchors. To evaluate the performance of a statically indeterminate structure under different earthquake intensities, a series of pseudo-dynamic, quasi-static cyclic and vibration tests were carried out at the European Laboratory for Structural Assessment of the Joint Research Centre at Ispra, Italy. The identified modal parameters from forced vibration tests at three different damage levels were used in order to quantify local and global damage indices by updating a 3D FE model of the structure with the non-linear Powell's Dog-Leg optimization method. Then, the Latin Hypercube Sampling technique, a variant of the Monte Carlo method, was employed to study the sensitivity of the updated parameters of the 3D model to modal inputs, caused by measurement noise. Rotations of beam-to-column joints and column bases, storey displacements and forces were employed during the final cyclic test in order to update a 2D FE model of the test structure. To avoid numerical instabilities during the detection of the non-linear behaviour of the structure, a novel technique based on the transformation of the origin coordinates in each half cycle was implemented. The identified joint behaviours allowed low-cycle fatigue energy-based damage indices to be applied. Copyright © 2009 John Wiley & Sons, Ltd.

Vulnerability of Turkish Low-Rise and Mid-Rise Reinforced Concrete Frame Structures

In this study, seismic safety of low–rise and mid–rise structures, which constitute approximately 75% of the total building stock in Turkey, is investigated by generating fragility curves. The scope is 3, 5, 7, and 9–story reinforced concrete moment resisting frame structures. The uncertainties in material variability and the specific characteristics of construction practice in Turkey are taken into account in the formation of structural simulations. Two-dimensional analytical models are constructed accordingly and categorized as poor, typical, or superior corresponding to the observed seismic performance of structures after major earthquakes in Turkey. The seismic demand statistics in terms of maximum interstory drift ratio are obtained for different sets of ground motion records by performing nonlinear time history analyses. The capacity is determined in terms of limit states and the corresponding fragility curves are obtained from the probability of reaching or exceeding each limit state for different levels of ground shaking. The generated fragility curves are employed in a preliminary evaluation application. For this purpose, Fatih, a highly populated earthquake–prone district in Istanbul, is selected. This study attempts to be a benchmark for future fragility based studies on earthquake damage and loss estimation in urban areas of Turkey.

Seismic design of beam-column joints in RC moment resisting frames - Review of codes

The behaviour of reinforced concrete moment resisting frame structures in recent earthquakes all over the world has highlighted the consequences of poor performance of beam column joints. Large amount of research carried out to understand the complex mechanisms and safe behaviour of beam column joints has gone into code recommendations. This paper presents critical review of recommendations of well established codes regarding design and detailing aspects of beam column joints. The codes of practice considered are ACI 318M-02, NZS 3101: Part 1:1995 and the Eurocode 8 of EN 1998-1:2003. All three codes aim to satisfy the bond and shear requirements within the joint. It is observed that ACI 318M-02 requires smaller column depth as compared to the other two codes based on the anchorage conditions. NZS 3101:1995 and EN 1998-1:2003 consider the shear stress level to obtain the required stirrup reinforcement whereas ACI 318M-02 provides stirrup reinforcement to retain the axial load capacity of column by confinement. Significant factors influencing the design of beam-column joints are identified and the effect of their variations on design parameters is compared. The variation in the requirements of shear reinforcement is substantial among the three codes.