Drift Capacity Research Articles

A locally weighted machine learning model for generalized prediction of drift capacity in seismic vulnerability assessments

AbstractDrift capacity of reinforced concrete (RC) columns is an important indicator to quantify the seismic vulnerability of RC frame buildings; however, it is challenging to accurately predict this value as the nonlinear behavior can vary greatly by column type. This article proposes a novel, local machine learning (ML) model, called locally weighted least squares support vector machines for regression (LWLS‐SVMR), which integrates LS‐SVMR and locally weighted training criteria to enhance and generalize the prediction of the drift capacity of RC columns, regardless of the type. A database of 160 circular RC columns covering flexure‐, shear‐, and flexure–shear‐critical specimens was developed to train and test the proposed LWLS‐SVMR. The proposed LWLS‐SVMR was validated by comparison with popular existing global and local learning approaches as well as a traditional empirical equation, and the results demonstrated that the proposed LWLS‐SVMR is superior to all other approaches and thus, is a promising artificial intelligence technique for enhancing the prediction of drift capacity, universally across RC flexure‐, shear‐, and flexure–shear‐critical columns. The LWLS‐SVMR exhibits capabilities which may yield it a feasible approach to predict complex, nonlinear behavior in a broad‐spectrum manner.

Large-scale quasi-static testing of precast bridge column with pocket connections using noncontact lap-spliced bars and UHPC grout

A novel pocket connection was put forward to be utilized in both ends of a precast bridge column to connect cap beam and foundation, respectively. The pocket connection adopted noncontact lap-spliced bars and ultra-high performance concrete (UHPC) grout. One 1:2.5 scale specimen was fabricated and tested to investigate the seismic performance of the precast bridge column with the proposed pocket connections. Based on OpenSees platform, a verified finite element model was utilized to simulate cyclic behavior of a monolithic reinforced concrete companion. The comparison was carried out to evaluate the precast bridge column in a comprehensive way. The results show that drift capacities of the two bridge columns are up to 5% and controlled by lateral force degradation. The lapped length of five times diameter is feasible when UHPC grout is used for longitudinal bars with a diameter no more than 32 mm. For the precast bridge column, the joint opening between column and foundation contributes over 30% to total lateral displacement and traditional equivalent plastic hinge model may be not suitable. With drift ratio over 1.5%, the precast specimen has larger secant stiffness than that of the monolithic companion, owing to the shorter shear length of the precast specimen caused by moving up of the actual plastic hinge region. The precast and monolithic bridge columns have good energy dissipation capacity, and the maximum damping ratios reach up to 19.8% and 22.6% at 5% drift ratio, respectively. The precast specimen has 18.8% less residual drift ratio at 5% drift ratio than the monolithic companion.

Seismic behavior of post-tensioned precast wide U beam–column interior joint: a finite element study

Due to many advantages over the traditional construction, wide beam–column system has gained the popularity in low–moderate seismic zones. However, the performance of this system in the region of higher seismicity is still questionable. This paper presents the seismic behavior of a typical post-tensioned composite wide beam–column interior joint and relevance of its implementation in different seismic zones of Thailand. The post-tensioned wide beam–column system studied in this paper consists of precast U beam with embedded A-trusses, precast column and cast-in-situ concrete poured over the precast U beam and in the joint region. In this paper, a 3D finite element (FE) model of the full-scale post-tensioned precast wide U beam–column interior joint was developed using the validated constitutive material laws and appropriate boundary conditions in LS-DYNA FE code. The specimen was subjected to displacement-controlled lateral cyclic load. The results of this study revealed force–displacement hysteresis behavior and failure pattern of the U beam–column interior joint. In addition, parametric study was carried out to investigate contribution of the major parameters designed for joint region to the drift capacity and strength of the joint. The drift capacity of the joint was found to be 2.2%, which partially fulfilled the drift demand from various seismic zones of Thailand. Further, a strong-column weak-beam failure mode was exhibited by the analyzed joint.

Numerical and analytical investigation of internal slab-column connections subject to cyclic loading

Properly designed flat slab to column connections can perform satisfactorily under seismic loading. Satisfactory performance is dependent on slab column connections being able to withstand the imposed drift while continuing to resist the imposed gravity loads. Particularly at risk are pre 1970’s flat slab to column connections without integrity reinforcement passing through the column. Current design provisions for punching shear under seismic loading are largely empirical and based on laboratory tests of thin slabs not representative of practice. This paper uses nonlinear finite element analysis (NLFEA) with ATENA and the Critical Shear Crack Theory (CSCT) to investigate the behaviour of internal slab-column connections without shear reinforcement subject to seismic loading. NLFEA is used to investigate cyclic degradation which reduces connection stiffness, unbalanced moment capacity, and ductility. As observed experimentally, cyclic degradation in the NLFEA is shown to be associated with accumulation of plastic strain in the flexural reinforcement bars which hinders concrete crack closure. Although the NLFEA produces reasonable strength and ductility predictions, it is unable to replicate the pinching effect. It is also too complex and time consuming to serve as a practical design tool. Therefore, a simple analytical design method is proposed which is based on the CSCT. The strength and limiting drift predictions of the proposed method are shown to mainly depend on slab depth (size effect) and flexural reinforcement ratio which is not reflected in available empirically-based models which appear to overestimate the drift capacity of slab-column connections with dimensions representative of practice.

Drift Capacity of RC Structural Walls with Special Boundary Elements

Drift Capacity of RC Structural Walls with Special Boundary Elements

Experimental Study on the Seismic Capacity of Anchored Brick Veneer on Nonstructural Masonry Walls

The seismic performance of anchored brick veneer with a newly developed tie metal assembly in the nonstructural masonry wall was evaluated experimentally in this study. The test specimens were manufactured with dimensions of 2.2 m × 2.02 m. The experimental variables were the arrangement of the tie metal assembly (orthogonal or staggered), the spacing of the tie metal assembly, and the size of the vertical locking bars. All the test specimens with tie metal assemblies were capable of supporting the equivalent static load based on the Korean Building Code, and retained a drift capacity of more than 2% corresponding to the performance level of life safety. The vertical locking bars improve the seismic performance of anchored brick veneer moderately, and the recommended spacing of the tie metal assembly is 800 mm × 400 mm. Keywords: Nonstructural Masonry Wall, Anchored Brick Veneer, Wall-Tie, Seismic Capacity, Experimental Study

Experimental study and parameter analysis on the seismic performance of self-centering hybrid reinforced concrete shear walls

To enhance the energy dissipation ability of self-centering shear walls, various types of dampers can be incorporated into the rocking surface of a reinforced concrete (RC) wall, which is called a self-centering hybrid shear wall. This paper focuses on self-centering hybrid RC shear walls, which are self-centering shear walls with partially unbonded mild steels. A cyclic loading test was carried out to study the seismic behavior of this type of shear walls compared with conventional precast RC shear walls. The test results showed that the self-centering hybrid RC shear walls displayed better deformation ability and re-centering ability. A multi-truss element model was used to simulate test results in the OpenSees software. To further study the seismic performance of self-centering hybrid RC shear wall, a parameter analysis was performed considering five parameters: wall aspect ratio, initial stress of post-tensioned (PT) tendons, the total area of PT tendons, the total area of mild steels, and yielding tensile strength of mild steels. The results of the parameter analysis showed that the most efficient method for improving the energy dissipation ability of the self-centering hybrid RC shear wall was increasing the area of mild steels. The parameter analysis also revealed that the drift capacity in the yielding state can be improved remarkably with the increase of the wall aspect ratio, as well as that the initial stress of PT tendons should be restricted.

Empirical drift-fragility functions and loss estimation for infills in reinforced concrete frames under seismic loading

Earthquakes that have occurred in the last twenty years in the Mediterranean area have had significant economic and social impacts. Most of the economic losses of reinforced concrete (RC) frames was due to nonstructural component damage, particularly masonry infills and partitions. Therefore, the seismic behaviour of masonry infills should be reliably characterized. The main goals of this study for a more reliable loss estimation for infilled RC frames are: (i) the analysis of the inter-story drift ratio (IDR) capacity at given damage states (DSs) with the aim to define drift-based fragility functions and (ii) analyse direct losses due to infill damage following seismic events. First, a database of experimental tests performed on 1-bay, 1-story scaled RC frames infilled with clay bricks or concrete blocks is collected. Drift-based fragility curves are obtained, which depend on the infill brick materials and properties. Then, the drift capacity threshold at each DS is correlated to the in-plane response of the infill panel to directly quantify the relationship that exists among them. The influence of openings on drift capacities is also evaluated. Then, seismic losses related to infills are computed, providing expected monetary losses depending on the infill typology. The required reparation activities and their costs are also listed. The bearing of each activity and cost at each DS is explicitly evaluated. Additionally, loss functions that directly depend on IDR demand are provided, thus fusing together the damage analysis and loss analysis. Finally, a simplified formulation for loss functions is proposed for a simple, practice-oriented loss calculation.

Evaluation of earthquake load resistance of masonry infilled RC frames using linear and non-linear dynamic analysis

The understanding of the dynamic behavior of structures is essential to design them to resist the lateral loads due to earthquakes. Recent past earthquakes have demonstrated the importance of proper designing of structural members to avoid damages in the buildings and loss of life. Generally the lateral load resistance of masonry infilled moment resisting frames is achieved by frame action and truss action. In this paper the seismic performance of a G + 9 storeyed masonry infilled RC framed building is evaluated by linear and non-linear dynamic analysis. The analysis is carried out using the finite element software-ETABS. The response spectrum and time history pertaining to the specifications as given in the Indian Seismic Code IS 1893:2016 is considered for the analysis. Three different frame models are studied namely, bare frame, fully infilled frame and soft storey frame to understand the lateral load resistance of the frames. The dynamic characteristics of the frames such as time period, frequency, mode shapes, storey displacements, inter-storey drift, over-turning moments and energy dissipation capacity are evaluated and compared. The fully infilled frame shows better seismic behavior than that of other two frames though it attracts more forces.

Reversed horizontal cyclic loading tests of flat slab specimens with studs as shear reinforcement

The results of a series of experiments on four reinforced concrete flat slab specimens with shear studs and a control specimen without any shear reinforcement are presented. The specimens were tested under constant gravity loads and reversed horizontal cyclic displacements. The main test variables were the applied gravity load and the number of perimeters of studs. One of the specimens was tested in two phases to study the postearthquake behavior. Results showed a considerable improvement of the deformation capacity of specimens with studs compared to the reference specimen. In agreement with previous research, increasing the applied gravity shear ratio resulted in a lower experimental drift capacity. It is shown that a better explanation of the observed ultimate drifts can be made by considering also the flexural capacity and the extent of shear reinforcement. The specimen tested in two phases exhibited considerable residual capacity, even after severe horizontal loading.

Seismic design and performance evaluation of self-centering timber moment resisting frames

Motivated by the recent concept of seismic resilient structures and societies, the seismic resilient timber solutions were developed to provide the lateral drift capacity while reducing the structural damage through controlled rocking and self-centering motion. However, very limited studies have evaluated the seismic performance of the post-tensioned self-centering timber frame at the building level, restricting the real-world applications of such structure. This study provides a post-tensioned self-centering timber frame solution for a building hypothetically designed in a high seismic zone in China. Besides, the same architectural design is provided with another comparable structural solution, i.e., a typical post and beam frame system with timber braces, conforming to the design code requirements. Subsequently, the nonlinear numerical models are carefully developed and their crucial component behaviors are calibrated with the existing experimental results. Finally, the seismic performance of the two structural solutions are systematically evaluated. The peak inter-story drift, the residual inter-story drift, and the Park-Ang damage index at the system level are investigated. Moreover, the fragility curves are generated demonstrating the self-centering feature of the seismic resilient timber solution. The advantages as well as challenges of such post-tensioned self-centering timber frame structures are clearly captured in the study.

Response of thin lightly-reinforced concrete walls under cyclic loading

During the last two decades, thin concrete walls have been frequently used to brace mid- to high-rise buildings in some Latin American countries. This structural system differs significantly in terms of wall geometry and reinforcement layout from traditional cast-in-place reinforced concrete wall buildings. Limited experimental data on this wall system and the absence of post-earthquake field observations make it difficult to assess whether such walls behave similarly to the walls designed according to the current local design code. The paper presents and discusses the results of an experimental program comprising quasi-static cyclic tests of four slender, thin and lightly-reinforced concrete walls with different geometrical configurations, steel properties and reinforcement layouts, which correspond to a common construction practice in Colombia. The seismic response of the specimens was assessed in terms of crack propagation and failure modes, hysteretic and backbone curves, contribution of rocking, flexural, shear and sliding components to lateral drift, stiffness degradation, and energy dissipation capacity. The results suggest that the response of these reinforced concrete walls does not meet the performance specified in the Colombian regulation if they are designed to reach the maximum lateral drift allowed by the code.

Probabilistic mainshock-aftershock collapse risk assessment of buckling restrained braced frames

Buckling-Restrained Braced Frames (BRBFs) are among the common seismic resistant systems with many beneficial characteristics such as stable cyclic behavior and high energy dissipation. However, recent studies have shown that BRBFs are susceptible to residual deformations during earthquakes which makes them vulnerable to aftershock events. The aim of the current study is to investigate the aftershock collapse capacity of BRBFs. In the first part of the paper, simplified procedures including IDA and collapse fragility analyses are carried out to gain more insight regarding the residual drift and collapse capacity of the intact frames. Then, aftershock fragility assessment is conducted for several damage states, to highlight the influence of post-mainshock residual drifts on the collapse of the structures. As for the second part, a detailed probabilistic framework is introduced and utilized to include the effects of upcoming aftershocks on the annual collapse probability of the structures. Results show that aftershock can highly intensify the structural response especially when the structure tolerates large residual drifts during the mainshock.

DEGAS: An innovative earthquake‐proof AAC wall system

AbstractBackgroundThe in‐plane response of infill walls independent of the material used has been investigated thoroughly in the literature and the common observation on the response was the formation of both compression struts and tension struts. These struts in the diagonals of the infill walls are the main reason for the cracking and crushing of the infill wall material. Researchers have proposed some techniques that enhance the performance of infill walls. Most of the proposed methods include a special device or connection detailing to isolate the infill wall from the RC frame even during excessive lateral displacement demands.AimThe objectives of the current study are: to devise and test a seismic isolation system for AAC infill walls that is capable of eliminating the damage due to in‐plane demands while being stable under out‐of‐plane demands. The outcomes of this study are believed to provide a sound alternative for constructing earthquake safe AAC infill walls.Materials & MethodsIn this study, a new method is devised to protect and enhance the performance of AAC infill walls, i.e. DEGAS. The DEGAS system is thought to increase both the ductility of the AAC infill walls in in‐plane demands and to stabilize the AAC infill wall during out‐of‐plane demands. To this end, an experimental program was formed to investigate the IP and OOP interaction for AAC infill walls with the application of the DEGAS system. In the scope of this study, three different tests were conducted to simulate i‐ IP only, ii‐ OOP only and IP + OOP cases. Two‐way cyclic displacement excursions were applied to the test specimens to mimic the in‐plane demands. Furthermore, uniform pressure was applied to simulate the OOP related demands. The OOP demands are considered by applying OOP pressure.ResultsSome crushing was observed during the testing of the Specimen S1. However, no visible cracks were detected in the AAC infill wall. This observation could be attributed to the application of DEGAS system along with the presence of the gap between the AAC infill wall and the RC frame. The maximum out‐of‐plane load of the Specimen S2 was determined to be about 20 kN. No sudden collapse‐type failure was observed in this test. This showed the importance of the application of the DEAGS system. Because, the out‐of‐plane failure of the AAC infill walls are generally total or partial sudden collapse of the wall. The Specimen S3 had a drift capacity of 2.5%. At this drift limit, the capacity reduction was determined to be only 8%. In addition, no sudden out‐of‐plane collapse of the infill wall was observed during the testing of Specimen S3.Discussions & ConclusionsIn this study, three half‐scaled tests were conducted on AAC infilled frames with the DEGAS system. The DEGAS system was shown to increase the stability of the AAC infill walls as none of the specimens was observed to fail by total or partial collapse of the AAC infill wall. In addition, the cracking of the AAC infill walls were also limited at drift ratios of about 2%, which is the drift limit for TEC 2007. This proved that the AAC infill with the DEGAS system would not show premature cracking at lower demands. The only observed damage was the disintegration along the interface of the AAC infill wall after 1.5% drift ratio.

Drift capacity of high-strength concrete columns with mixed-grade longitudinal reinforcements

A unique reinforced concrete column design method which aims to improve the ductile behavior of reinforced concrete columns by utilizing various steel grades for longitudinal reinforcements is evaluated in this article. Six large-scale reinforced concrete columns were tested, with the columns subjected to axial load and cyclic forces under reversed bending. The parameters varied in the test program including the axial loading level and the ratio and strength of longitudinal steel reinforcement. It was found from the test results that utilizing longitudinal high-strength steel reinforcement by the ratio of 30%, 50%, and 100% of the total longitudinal reinforcement in a column section will increase the lateral loading drift capacity by 18%, 26%, and 55% on average, respectively. Parametric studies via nonlinear finite-element approach were performed to study the influence of various design parameters on the ultimate drift capacity of reinforced concrete columns. The correlation between the ultimate drift capacity and the confinement level, the axial loading level, and the ratio and grade of longitudinal high-strength reinforcing bars was investigated. Design charts for various ultimate drift levels in terms of other design parameters were developed.

Shear behavior of adobe and rammed earth walls of heritage structures

In Colombia and other South American countries, most structures in the colonial period were built with adobe and/or rammed earth masonry. During past earthquakes, some of these structures collapsed even with moderate magnitude earthquakes resulting not only in significant loss of human lives, but also in large economic, cultural and heritage losses. The assessment of the seismic vulnerability of these historic buildings requires knowledge of the in-plane and out-of-plane capacity of the shear walls that constitute the structural system of the construction. In this investigation, the in-plane shear capacity is addressed by conducting cyclic tests on six 2.50 m × 1.80 m × 0.40 m solid walls and two 7.00 m × 3.45 m × 0.60 m walls with openings built with adobes obtained from a mid-nineteenth century construction and rammed earth with properties similar to those heritage buildings of Colombia. The experimental program involves variations in the vertical load and the construction material of the specimens. The effect of windows and doors openings in the shear capacity of the specimens is also evaluated. The experimental results show that: (a) failure mechanisms of earthen walls are dominated by the presence of diagonal cracks that divide the walls into large segments that eventually will fall off leading to loss of shear capacity; (b) shear capacity is controlled by the wall axial load and aspect ratio; (c) lower bounds of local drift capacity at initial cracking and peak shear strength of the walls and piers are 0.08% and 0.80%, respectively. Finally, based on the experimental results of this investigation and others available in the literature, a simplified expression is proposed to estimate shear capacity of earthen walls considering their axial load and aspect ratio.

Seismic-resistant self-centering rocking core system with buckling restrained columns

Conventional concentrically braced frame (CBF) systems have limited drift capacity prior to brace buckling, and related damage leads to deterioration in strength and stiffness. CBFs are also susceptible to soft-story failure. A pin-supported self-centering rocking core system with buckling-restrained columns (SCRC-BRC) is being developed to provide significant drift capacity while limiting damage due to residual drift and soft-story mechanisms.The SCRC-BRC system consists of beams, columns, and braces branching off a central column, with buckling restrained columns (BRCs) incorporated into the system at the first story external column positions. The BRCs and friction generated at lateral-load bearings at each floor level are used to dissipate energy to reduce the overall seismic response of the SCRC-BRC system. Vertically-aligned post-tensioning bars provide additional overturning moment resistance and aid in self-centering the system to eliminate residual drift. The pin support condition at the base of the central column and the lateral stiffness of the system enable it to exhibit a nearly uniform inter-story drift distribution.In this study, the suite of 44 DBE-level ground motions used in FEMA P695 is numerically applied to several SCRC- BRCs to demonstrate the seismic performance of the system. The results show that the SCRC-BRC system has a nearly uniform inter-story drift response, high ductility, and a high energy dissipation capacity, and is an effective seismic-resistant system.

CYCLIC BEHAVIOUR OF LIGHTLY REINFORCED CONCRETE COLUMNS WITH NON-DUCTILE LAP SPLICES

Experimental testing of lightly reinforced concrete column was conducted to investigate the collapse behavior of such column under cyclic lateral loading. Six column specimens, which have low longitudinal reinforcement and lack of confinement, were detailed with no lap splice, and non-ductile lap splice within or outside critical region. Placing the short, unconfined column's lap splice within critical region caused peak moment to fall short under its nominal moment capacity. In contrast, moment capacity of the specimen containing non-ductile lap splice outside critical region was in close agreement with those of specimen without lap splice. However, its inelastic damage region was moving away from the beam-column interface, resulted in degradation of drift capacity and rapid degradation of lateral strength. The presence of non-ductile lap splice outside critical region also potentially shift column's collapse mechanism from flexure to flexure-shear critical. The ability of lightly reinforced concrete columns to maintain its axial load carrying capacity to large drift ratios despite heavy damage and significant loss of lateral load carrying capacity indicates that lap splice failure does not create sudden collapse hazard.

Cyclic loading test of self-centering precast segmental unbonded posttensioned UHPFRC bridge columns

Three 1/3-scale precast segmental bridge columns, manufactured with ultrahigh-performance fiber-reinforced concrete (UHPFRC) incorporating river sand and coarse aggregate, were tested under cyclic loading. Energy dissipation (ED) bars, embedded in ultrahigh-performance concrete (UHPC) grout, maintained continuous across segment joints and unbonded at the bottom joint. Self-centering prestressing force was provided by unbonded posttensioning (PT) tendons. The research parameters included PT force level and the amount of ED bars. Test results showed that all the specimens exhibited no less than 8% drift capacities, which were remarked with the first fracture of ED bars. No obvious cracking and limited UHPFRC spalling were observed. Both PT force level and the amount of ED bars have notable effects on stiffness, lateral strength, and ductility. Increased PT force may improve ductility with the total axial loading ratio less than 0.08. All PT tendons were elastic and no yield or rupturing was found, but the stress loss was significant. The equivalent unbonded length can be evaluated with 0.007dbfy for ED bars embedded in UHPC grout. The rotation of the bottom joint dominated lateral deformation and the contribution of joint sliding can be neglected. The contribution λED of ED bars to lateral strength should be no more than 25% to maintain self-centering capacity.

Economic Feasibility Study of Self-Centering Concentrically Braced Frame Systems

AbstractSelf-centering concentrically braced frame (SC-CBF) systems have been developed to increase the drift capacity of conventional concentrically braced frame (CBF) systems prior to damage to r...