High Seismic Performance Research Articles

Seismic resistance analysis and optimization of gymnasium truss structure

The gymnasium is mainly composed of truss structure, with a large span, and requires high seismic performance. To ensure greater stability of the truss structure, modal analysis was conducted on the mechanical model, yielding the natural frequencies and modal shapes. In order to improve the seismic performance, BRB rods were added to the support points, and the frame structure was reinforced with diagonal braces. Through modal verification, it can be seen that the stiffness of the truss structure was significantly improved. The internal forces of the truss were simulated under the El Centro and Taft seismic wave conditions. The results show that the optimized structure can significantly reduce the internal forces and improve the overall seismic performance. The fundamental natural period of the reinforced structure is less than that of the unreinforced structure, and the stiffness of the reinforced steel structure increases, making it more sensitive to vertical seismic motion.

NONLINEAR SIMULATIONS TO EVALUATE THE CODE-BASED RESPONSE MODIFICATION FACTOR FOR SEISMIC DESIGN OF SLAB-ON-PILE STRUCTURE

Slab on Pile (SOP) structure using concrete spun pile (CSP) is frequently constructed for highway or railway infrastructures in Indonesia. However, some previous studies showed that spun piles have low energy dissipation and ductility. Therefore, spun pile application as bridge piers, particularly in high seismic locations such as Indonesia, needs additional consideration. The response modification factor (R) in the SOP elastic seismic design needs to be carefully considered since this parameter reflects the ability of the structure to dissipate energy through inelastic behavior. The work discussed in this paper primarily concerns the evaluation of the R-value based on the Indonesia seismic bridge design code, SNI 2833-2016, which is applied to SOP seismic design. The study provided an alternative reference for engineers in the seismic design of a SOP structure. Preliminary elastic design of SOP structures demonstrated that the number of piles and structural flexibility is significantly affected by the R-values consideration. In addition, the pinching hysteresis captured from the nonlinear dynamic analysis results emphasized the limited capability of an SOP structure in dissipating energy under seismic excitation. Moreover, the spun pile concrete material, especially in the pile-to-pile head connection, was observed to have an earlier failure. This study strongly suggested using an R-value of 1.5 to achieve a high seismic performance SOP structure with little need for aftershock retrofitting, even though this would necessitate much more spun piles. However, some further research could be conducted to develop the high seismic performance but economical design of SOP structures.

Numerical and experimental investigation of a new model of friction damper in diagonal brace under cyclic loading

Owing to the performance of prefabricated friction dampers, which are rapidly increasing, the resistance of structural systems against earthquakes increases and depreciates the energies generated by earthquakes in the structure. It is important to use passive control systems to control the vibrations of a structure at a single level. However, in the design, they cannot depreciate the incoming energy from earthquakes at different levels. Friction dampers focus on displacement variables and are mostly used in steel structures according to the rules of a Coulomb damper or a friction brake that converts kinetic energy into heat through friction. In this study, a new type of friction damper, called a flat cylindrical friction damper, was designed using brake pads in a diagonal brace. The performance and seismic resistance of this system, as well as the amount of energy loss, were investigated. In this study, 18 laboratory tests were conducted using the universal device to check the research variables, their hysteresis diagrams were shown, and the configuration of the damper was designed such that grooved bolt connections and twin steel cables of different sizes and thicknesses were used. Moreover, the way the internal and external components are placed in the damper is such that innovation in tension and pressure has been created. In addition, the movement of the cylindrical element in the damper increased the amount of friction, owing to the presence of two types of brake pads with friction coefficients of 0.11 and 0.16 and the bolt connections. This demonstrates the damper performance under different sliding forces at different friction levels. The geometric dimensions, thickness of the brake pad, number and size of bolts, diameter of cables, sliding force, and location of the damper were among the variables investigated in this study. Brake pads, steel cables, and bolt connections are important and economically affordable. The seismic performance of the intended frame was investigated using 80 different damper models and the placement of the research variables. The desired optimal models were modelled using Abaqus software, analysed, and designed. This system aims to reduce the relative horizontal displacement of floors and increase the amount of energy absorption. An increase in theaxial-force created in multiple loading cycles always causes damage to damper components and frames. In this study, we used a special multi-level geometry to reduce the axial-force created in the damper, the relative displacement of the frame, and damages in the elements, as well as increase the ductility. The results show that the friction surfaces of steel plates and brake pads is very high due to the displacement and damping of the cables. Additionally, with the consumption of energy and its absorption by the damper in cyclic loads, displacement is easily controlled. The seismic response of the structures in terms of frame and damper displacement, base shear forces, and energy absorption is also observed. Numerical studies confirmed that the intended damper is an independent seismic-resistant member in critical building structures when high seismic performance or seismic resilience during moderate and strong earthquakes is desirable.

Experimental study and design method of embedded concrete-filled rectangular steel tube column base under cyclic load

Embedded column base has been widely used in concrete-filled steel tube (CFST) structures due to its high rigidity and good seismic performance. However, the strength analysis of the embedded CFST column base was not yet clear since there was little experimental research on it. In this paper, the experimental investigations of six embedded concrete-filled rectangular steel tube (CFRST) column bases under constant axial load and cyclic load were carried out to study the effects of embedded depth, improvement measures and axial compression ratios on the seismic performance of the column bases. The experimental results indicated that setting stiffeners, increasing the embedded depth or axial compression ratios could improve the seismic performance of the column base. In this experiment, the critical embedded depths of the columns with or without stiffeners were 0.7 and 1.5 times the column width B respectively. When the embedded depth was 0.7B, the contribution of anchor bolts to the moment resistance capacity of the column bases could reach up to 14.2%. Based on the analysis of the force transmission mechanism between the column and the concrete foundation in the embedded CFRST column base, a design method considering the contribution of different components to the moment resistance capacity of the CFRST column bases is proposed. The prediction results are in good agreement with the tested results and collected data, within ± 15% error. The parameter analysis based on the design method has revealed the influence patterns of various parameters on the moment resistance capacity of the column bases.

Seismic Performance and Calculation Method of Precast Reduced Beam Section Connection

To prevent brittle damage and improve the post-earthquake rapid repair capability of beam–column connections, a precast reduced beam section (PRBS) connection joint that can be rapidly repaired under earthquake action was proposed in this study. Four specimens, including a repaired specimen, were subjected to a quasi-static test to investigate the seismic performance and repair ability of the connection. Seismic performance indices such as the failure mode, hysteresis curve, skeleton curve, strain distribution, and ductility were obtained through observations and analyses. The results indicated that the novel connection exhibited superior load-bearing, energy dissipation, and rotation capacities, compared to the welded flange-bolted web and traditional bone-weakened connections. This novel connection effectively relocated the plastic hinge to alter the failure mode and prevent brittle damage. Additionally, rapid post-earthquake repair was achieved by replacing the dog-bone-style splice section, maintaining a high load-bearing capacity and seismic performance. Finite element (FE) models were established to analyze the mechanical behavior of the specimens, and a parametric analysis was conducted to study the influence of different parameters on the load-bearing capacity of the connection. Based on the experimental and FE analysis results, the possible yield and failure modes of the connection were analyzed, and a calculation method for the bearing capacity of the PRBS connection was proposed. A comparative result demonstrates that the proposed calculation method can accurately predict the load-carrying capacity of a connection.

Shaking table tests of veneer masonry wall retrofitted with long-rawlplug screw anchors

Veneer masonry walls are vulnerable to lateral forces such as seismic loads, and their failure has caused human casualties and property damage. This study developed a new anchor for existing veneer walls and evaluated its seismic performance using shaking table tests. The presence or absence of retrofit anchors, combination of anchors and steel strips, and anchor spacing were considered as the experimental variables. Out-of-plane excitation was applied to the specimens, and the magnitude of the seismic acceleration was calculated according to the required response spectrum defined in ICC-ES AC156. The experimental results showed that overturning occurred on the non-retrofitted veneer wall; however, the veneer wall reinforced using the proposed anchor exhibited no overturning. The peak ground acceleration, relative displacement, amplification coefficient, and shear force of the reinforced specimens decreased relative to those of the unreinforced specimens. Notably, the proposed method achieved a high seismic reinforcement performance even when the anchor spacing was set to 800 mm.

Axial Compressive Behavior of Cross-Shaped CFST Stub Columns with Steel Bar Truss Stiffening.

Concrete-filled steel tube (CFST) columns have been widely used in residential buildings due to their high bearing capacity, good ductility, and reliable seismic performance. However, conventional circular, square, or rectangular CFST columns may protrude from the adjacent walls, resulting in inconvenience in terms of the arrangement of furniture in a room. In order to solve the problem, special-shaped CFST columns, such as cross-shaped, L-shaped, and T-shaped columns, have been suggested and adopted in engineering practice. These special-shaped CFST columns have limbs with the same width as the adjacent walls. However, compared with conventional CFST columns, the special-shaped steel tube provides weaker confinement to the infilled concrete under axial compressive load, especially at concave corners. The parting at concave corners is the key factor affecting the bearing capacity and ductility of the members. Therefore, a cross-shaped CFST column with steel bar truss stiffening is suggested. In this paper, 12 cross-shaped CFST stub columns were designed and tested under axial compression loading. The effects of steel bar truss node spacing and column-steel ratio on the failure mode, bearing capacity, and ductility were discussed in detail. The results indicate that the columns with steel bar truss stiffening can change the final deformation mode of the steel plate from single-wave buckling to multiple-wave buckling, and the failure modes of columns also subsequently change from single-section concrete crushing failure to multiple-section concrete crushing failure. The steel bar truss stiffening shows no obvious effect on the axial bearing capacity of the member but significantly improves the ductility. The columns with a steel bar truss node spacing of 140 mm can only increase the bearing capacity by 6.8% while nearly doubling the ductility coefficient from 2.31 to 4.40. The experimental results are compared with those of six design codes worldwide. The results show that the Eurocode 4 (2004) and the Chinese code CECS159-2018 can be safely used to predict the axial bearing capacity of cross-shaped CFST stub columns with steel bar truss stiffening.

Numerical Analysis of Low-Velocity Impact Behaviour of Protective Concrete-Filled Steel Plates Composite Wall.

In this research, a protective concrete-filled steel plate composite wall (PSC) is developed, consisting of a core concrete-filled bilateral steel plate composite shear wall and two lateral replaceable surface steel plates with energy-absorbing layers. The PSC wall is characterised by high in-plane seismic performance as well as out-of-plane impact performance. Therefore, it could be employed primarily in high-rise constructions, civil defence initiatives, and buildings with stringent structural safety criteria. To investigate the out-of-plane low-velocity impact behaviour of the PSC wall, fine finite element models are validated and developed. Then, the influence of geometrical and dynamic loading parameters on its impact behaviour is investigated. The results show that the replaceable energy-absorbing layer could significantly decrease the out-of-plane displacement and plastic displacement of the PSC wall due to its large plastic deformation, which could absorb a significantly large amount of impact energy. Meanwhile, the PSC wall could maintain high in-plane seismic performance when subjected to impact load. The plastic yield-line theoretical model is proposed and utilised to predict the out-of-plane displacement of the PSC wall, and the calculated results agree very well with the simulated results.

Experimental studies on structural performance of precast concrete shear walls with innovative UHPC-based connections

Ultrahigh-Performance Concrete (UHPC) is an advanced class of cement-based composite that offers excellent bond performance with steel bars. When compared to conventional approaches, using UHPC-based connections for Precast Concrete Shear Walls (PCSWs) has the advantages of smaller bar lap-spliced lengths and greater tolerance to installation errors. In this study, a two-stage scheme was proposed. Firstly, the bond properties between lapped steel bars and UHPC were determined to provide guidelines for designing PCSWs. A total of 15 pullout samples were designed and tested under direct tension. Failure patterns including steel bar pullout, cover splitting, and steel bar rupture were summarized. The basic splice length of steel bars with diameters limited to 14 mm in UHPC should be at least 6 times the bar diameter. In the second stage, the seismic performance of PCSWs with UHPC-based connections was investigated. Two full-scale PCSWs and two monolithic walls were constructed and tested cyclically in axial compression ratios of 0.1 and 0.3. In PCSWs, the splice length of additional bars (the one-row) in UHPC was set as 10 times the diameter to allow for a safe margin. PCSWs with UHPC-based connections demonstrated higher load-carrying capacity, better ability to dissipate energy, and comparable ductility to monolithic counterparts. An evaluation of test results also met the acceptance criteria for shear wall systems that could be considered as structures assigned to high seismic performance.

Triaxial shake table testing of an integrated low‐damage building system

AbstractLessons from recent earthquakes have provided a tough reality check of the traditional seismic design approach and technologies, highlighting the urgent need for a paradigm shift of performance‐based design criteria and objectives toward low‐damage design philosophy and technologies for the whole building system. Modern society is asking for “earthquake proof” resilient buildings that are able to withstand seismic events without compromising their functionality. The EU‐funded SERA (Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe Project) project discussed in this paper provided the opportunity to develop and validate within the European context an integrated seismic low‐damage prototype, including main structure and non‐structural elements, for the next generation of high‐performance buildings. This paper presents an overview of the research, involving three‐dimensional shake table tests of a two‐storey 1:2 scaled timber‐concrete post‐tensioned dissipative low‐damage structure “dressed” by earthquake‐resistant gypsum/masonry partitions and glass/concrete facades. Specimen details, construction and assembly phases, test setup, and experimental results are discussed. After many cycles of input motions at increasing levels of seismic intensity (higher than Collapse Prevention Limit State), the integrated building system exhibited a very high seismic performance. The experimental campaign carried out at the National Laboratory of Civil Engineering in Lisbon confirmed the unique potential of low‐damage technologies and the opportunity for their widespread implementation into design practice.

Seismic performance of buildings with novel self‐centering base isolation system for earthquake resilience

AbstractThis study presents a novel self‐centering (SC) base isolation system enabled by traditional lead rubber bearing (LRB) incorporating superelastic shape memory alloy (SMA) U‐shaped dampers (hereinafter referred to as SMA‐LRB). This system is particularly suitable for some important structures (e.g., hospital buildings) that require high seismic performance and rapid recovery of normal serviceability after a severe earthquake. The working mechanism of the SMA‐LRBs is first illustrated, followed by a comparative experimental study on the traditional LRB and the emerging SMA‐LRB. Test results confirm the satisfactory flag‐shaped hysteresis loops of SMA‐LRB associated with significantly reduced residual deformation under cyclic loading. Subsequently, a refined numerical modeling strategy for these bearings is developed. The seismic performances of the SMA‐LRBs are examined systematically through two comparative reinforced concrete (RC) frame buildings, namely, the traditionally isolated and the SC isolated cases under far‐ and near‐field earthquakes. Seismic fragility analyses are further carried out through incremental dynamic analysis (IDA). The seismic responses demonstrate that the SC isolated building can match or improve the behavior of the traditional isolated buildings. Compared with the considerable residual deformation of the traditional isolated system under some earthquake events, the SC isolated system exhibits negligible residual deformation that can significantly avoid normal serviceability disruption while achieving the high‐performance objectives. The SC base isolation system can provide a promising type of advanced seismic protection device for earthquake resilient design.

AN EXPERIMENTAL STUDY ON HORIZONTAL RESISTANT MECHANISM OF SANDWICHED PANEL STRUCTURE OF INSERTED METHOD

Recently, in Japan, there are some discussions to promote the use of timber resource in the field of architectural buildings. For examples, some latest mid-rise buildings are constructed using wooden material, such as the facilities of Tokyo Olympic 2020. We can experiment the dairy life and architectural space with timber materials, which often has attracted attention. In Japan, the demand of low-rise prefabricated steel building is recently increasing. However, to satisfy the seismic resistant performance of building, they are required to have lots of seismic resistant wall which restrict layout of wall and opening. The object of this study is to develop low-rise prefabricated steel building with high seismic resistance performance using hybrid structural system using wooden materials. We suggest the method of sandwich panel structures, which steel column is sandwiched by structural plywood connected by bolt joints. To improve productivity and seismic resistance, this paper suggests the construction process using inserted wall sliding construction method. To clarify the resistant mechanism and structural performance, a horizontal loading test is conducted. From the results, the resistant mechanism in the diagonal direction is appeared; it means that the effective resistant system can be obtained. Also, the composite effect of steel and plywood is presented to give the high strength and rigidity. From the observation of test results, the analysis model is assumed. And also, it is confirmed that the proposed model can evaluate the strength of test results.

Seismic Performance of Super High-Rise Building Structure with Dual Lines of Defense Based on Response Surface Optimization Algorithm

In order to improve the safety performance of supertall buildings under earthquake, a seismic performance analysis method of double lines of supertall buildings based on a response surface optimization algorithm is proposed. Firstly, the structural performance indexes of super high-rise buildings are selected, and on this basis, the material constitutive model is constructed by the structural elastic-plastic analysis method to complete the seismic design of the first line of defense. Then, the response surface method is used to optimize the material constitutive model and complete the seismic design of the second line. Finally, the anticollapse limit state analysis method is used to determine the seismic performance of the double line of super high-rise building structures. The experimental results show that the proposed analysis method has high seismic performance, and the axial compression ratio of wall and column is always stable, in which the column is always at about 0.5 and the wall is always at about 0.26, which lays a foundation for the safety performance of super high-rise building structures under earthquake.

Non Linear Analysis on CFDST columns with and without GFRP Wrapping

Abstract: Concrete Filled Double Skin Steel Tube (CFDST) columns are modified form of Concrete Filled Steel Tubular (CFST) columns, developed by several researchers. CFDST column composed of two concentric steel tubes in which concrete is packed in between them. It is available in various geometrical shapes. CFDST have many advantages such as high strength, high bending stiffness, good seismic and fire performance. But it is found that CFDST columns have some disadvantages including ageing of structures, corrosion of steel tubes etc. which reduces the strength of the column. So, to prevent these drawbacks and to strengthen the structure, Glass Fiber Reinforced Polymer (GFRP) can be used as an external cover. The present study aims to do nonlinear static analysis of CFDST columns having different hollow ratio wrapped with and without GFRP under axial compression using ANSYS finite element analysis software.

Experimental and numerical study on the seismic performance of rocking cold-formed steel frame

The poor seismic performance of thin-walled cold-formed steel (CFS) structures has been often observed in high seismic regions because of their low ductility, insufficient energy dissipation capacity. The work presented in this paper aims to improve the seismic performance of CFS and propose the innovative rocking cold-formed steel frame (RCFSF) by releasing the constraints at the foundation. Compared with the traditional cold-formed steel frame (CFSF), the RCFSF was installed with buckling restraint steel plates (BRSPs) to connect the columns and foundation, which can dissipate energy through the tensile and compressive deformation under the action of the earthquake. A pseudo-static test program was carried out to investigate the seismic performance of the one-third scaled single-bay three-story RCFSF. The results indicated that the plastic damage in RCFSF was greatly reduced and the ductility of the RCFSF can satisfy the seismic design requirements. The damage was mainly concentrated in BRSPs that can be easily replaced, and the local buckling of the beam-to-column joints was observed when loaded to the large lateral displacement. The numerical analysis was performed by ABAQUS, and the analysis results of the fine finite element model are consistent with the test results. It was found that the energy dissipation capacity of the RCFSF is better than those of the CFSF with the rigid column foot. With increasing the width of the beam flange, the local buckling of the beam-to-column joints can be reduced. The high seismic performance of the RCFSF can be achieved by rational design.

Seismic Retrofit Technique Using Plywood and Common Nails for Connections of Low-Rise Timber Frame Construction

Since the Japanese Building Standards Act was revised in 2000, the installation of steel timber connectors (STCs) to reinforce timber frame (TF) connections has been mandated for new-build TF houses in Japan. However, for the TF houses built before then, more than 40% do not have sufficient STCs and are considered earthquake-prone. This study proposed a simple and easy seismic retrofit technique for such earthquake-prone existing houses. The proposed technique can reinforce TF connections using only plywood and common nails and achieve equivalent performance to the benchmark STCs used in Japanese TF houses, such as the “CP-T type” or the combination of “VP type” and “BP type” STCs. Experiments were performed to compare the proposed technique with the STCs using pullout and full-scale in-plane cyclic tests. The experimental results showed that the proposed technique had a higher seismic performance than the STCs, which was particularly excellent in displacement ductility to prevent a collapse of the TF house without damaging the timbers. The proposed technique will be accepted by many carpenters when retrofitting earthquake-prone existing houses because simple and easy.

Analysis of Initial Cracking of an Interface between a Bundled Lipped Channel–Concrete Composite Wall and an Infill Wall

The bundled lipped channel–concrete (BLC-C) composite wall structure is a new structure with several advantages such as a high bearing capacity and good seismic performance. However, interface cracks between a BLC-C composite wall and the infill wall (non-structural wall) are a severe problem and need to be urgently resolved. Interface cracks affect not only the esthetics, but also the normal use of a building. The presence of interface cracks changes the perceptions of the owners of a structure, forcing them to question its safety and even take legal action against its developer. Therefore, in this study we aimed to investigate the initial cracking of the interface between a BLC-C composite wall and an infill wall. Unidirectional horizontal loading tests were conducted on two infill wall specimens constrained by BLC-C composite walls on both sides. The finite element analysis software ANSYS was used to simulate the loading process of the tests. The test results were compared to verify the accuracy of the finite element model. A finite element analysis was conducted to determine the effect of the horizontal displacement of the specimens when the interface initially cracked under different parameters such as the widths of the BLC-C composite wall, infill wall, and opening as well as the strength grade of the bricks and maximum normal contact stress. The results showed that a decrease in the width of the BLC-C composite wall or a rise in the width of the infill wall delayed the appearance of interface cracks. A large opening also delayed the occurrence of interface cracks. An enhancement in the strength grade of the bricks led to an earlier appearance of interface cracks. Interface cracks occurred later with an increase in the maximum normal contact stress between the BLC-C composite wall and the infill wall.

Seismic analyses for power transformers

Reliability and security of power systems, especially in areas prone to earthquakes, depends on the seismic withstand of its components and interaction of these components with other elements. All relevant power products and components should be designed and tested to guarantee high seismic performance. Option which is strongly recommended for seismic qualification is shake table test. This way is very expensive and in some cases like power transformers impossible due to its weight and size. Because of this the numerical analyses can be very helpful to determine the dynamic characteristic of the system. This way is more and more used during evaluation of seismic performance of power products, especially in the design phase. In the paper a different numerical approaches for seismic analyses of the power transformers have been presented. In the first part of the article focus was put on typical simulation methods defined by IEEE and IEC standards. This approach is dedicated only for transformer’s components. Due to fact that standards do not provide clear information about fluid influence on power equipment during seismic events, some investigations related with oil filled transformers were done and summarized. Three different numerical methods were investigated. First one is built based on the Fluid-Structure Interaction (FSI) methodology. In this approach combination of different software (CFD, structural, and coupling code) is used to cover phonemes related with fluid dynamics and structural analyses. FSI methodology gives a wide possibility but, it’s very complex however, is very complex which can be a disadvantage for very complex objects. Next one uses acoustic elements, where the fluid is modeled as acoustic medium. This is method which allows to take into account fluid during seismic simulations in simplified way. The last one uses Lagrange and Euler element formulations (CEL) in which sloshing effect of the oil in power products can be considered. All this approaches can be very helpful to determine the dynamic characteristic of the transformers and its equipment including fluid.

Numerical Study on Connections of Replaceable Shear Link with Inserted Pins

The link end plate of replaceable shear link in eccentrically braced frames has been modified with the ‘inserted-pins’ to ensure the high seismic performance and to reduce the number of bolts in its slip-critical connections. The maximum shear force in the connection is resisted by the pins, while the bolts resist the bending moment at the link-ends. Numerical work has been conducted using a non-linear ABAQUS program to study the deformation as well as the stress distribution of the shear-link and its connection elements: end plates, bolts, pins, and beam-outside the link. The results showed an adequate performance of the proposed modified shear link connections, where the end plate of the beam outside the link remained elastic as the shear-link reached 0.08 rad plastic rotation due cyclic loading.

Study on the Flexural Strength of Interior Thick Wall-Thick Slab Joints Subjected to Lateral Force Using Finite-Element Analysis

A brand-new structural type, termed thick wall-thick slab structure, has been developed in recent years based on the reinforced concrete wall structure in Japan. This type of structural system can not only maintain high seismic performance, but also provide large interior space and improve the flexibility of the architectural design that is more favored by architects. In the present study, an equivalent cross-sectional area concept in which a coefficient termed the equivalent cross-sectional area ratio is proposed to estimate the flexural strength of the horizontal member of the interior wall-slab joints, which are critical assemblies in the thick wall-thick slab structures. To capture the stress condition of slab flexural reinforcement for calculating the equivalent cross-sectional area ratio, the method of finite-element analysis was employed in this work. The finite-element modeling was calibrated firstly using two isolated interior wall-slab joints from literature and consequently applied to a parametric numerical study. Finally, results from these finite-element analyses are adopted to propose the equivalent cross-sectional area ratio for modifying the current code formula to predict the flexural strength of interior wall-slab joints in TWTS structures subjected to lateral force.