Ductility Ratio Research Articles

Flexural Response of Functionally Graded Rubberized Concrete Beams.

Recycling rubber and/or steel fiber components of waste tires in construction applications is a venue for maximizing the recycling rate of these items. Additionally, it supports the move towards producing sustainable construction materials and conserving natural resources. Previous research explored the viability of employing recycled waste rubber particles as an alternative for natural aggregate. Despite the adverse effect of rubber on the mechanical properties of concrete (e.g., lower compressive strength), it produces several advantages, including excellent dynamic and ductility properties, which can be utilized in structural members critical to dynamic loads, e.g., blasts, earthquakes, and impacts. In an effort to expand the adoption of waste rubber in concrete beams and to eliminate key concerns associated with the degradation of their flexural behavior, the functionally graded (FG) beams concept was utilized. The present investigation comprised the testing of five beams using a four-point bending configuration. Plain concrete, rubberized concrete (RuC), and steel-fiber reinforced rubberized concrete (SFRRuC) beams were cast along with FG beams arranged in two layers. The top layer of the FG beams comprised plain concrete, while the bottom layer consisted of RuC or SFRRuC. Experimental findings indicated that the flexural behavior of the FG beam with layers of SFRRuC and plain concrete exceeded the flexural strength, displacement ductility ratio, and toughness performances of the plain concrete beam by 9.9%, 12.9%, and 24.4%, respectively. The moment-curvature relationship was also predicted for the tested beam and showed an excellent match with the experimentally measured relationship.

Effects of annealing temperature on microstructure and mechanical properties of a low density δ-TRIP steel plate via intercritical quenching-annealing process

In this study, the effects of annealing temperature on microstructure and mechanical properties of Fe–9Mn–5Al-0.3C (wt.%) low density steel plates via intercritical quenching-annealing process were investigated through field-emission scanning electron microscopy, electron backscatter diffraction, X-ray diffraction, and tensile tests. The results showed that the experimental steel maintained micro-laminated microstructure after intercritical quenching-annealing treatment, consisting of δ-ferrite band and tempered martensite lamellar. After annealing at the range of 600–800 °C following quenching of 1050 °C, tempered martensite lamellar mainly changed, and affected the mechanical properties of the steel. The annealed experimental steels exhibited wide yield strength grades (460–620 MPa) with excellent ductility (40–63 %) and low yield-tensile ratio (0.65–0.75). The proportion of austenite, the density of geometrically necessary dislocations, and high-angle grain boundary density of tempered martensite region, as well as the presence or absence of carbides, were considered to contributed to the mechanical properties. Austenitic mechanical ability was analyzed. Various annealed temperature led to the different levels of austenitic stability through changing the enrichment of alloyed elements in austenite, further causing different degrees of TRIP effect. TWIP effect existed during deformation according to estimation of SFE. The steel annealed at 740 °C had maximum uniform elongation (62.4 %) and the highest product of strength and elongation (45.2 GPa%), depending on the maximum proportion of austenite transformed into martensite during deformation. However, the 680 °C annealed steel with the highest austenitic stability exhibited deficient TRIP effect, leading to the occurrence of necking. Moreover, work hardening behavior and fracture morphology of the experimental steel were analyzed.

Behaviour of Grouted Sleeve Wall Connection under Lateral Load

A grouted sleeve’s efficiency in splicing steel bars makes it a potential choice for connecting precast elements. While most studies have focused on the feasibility of grouted sleeves under tension, only a few have investigated the real response of precast concrete members connected using grouted sleeves. In this study, Tapered Head Sleeves (THS) were utilized as connections for precast walls. The objectives were to examine their behavior under incremental lateral loads and assess the feasibility of THS as a wall connection. Five test specimens and one control specimen were fabricated, each comprising two walls joined by THS. The load was applied 1.8 m above the joint until specimen failure. Specimens that experienced bar fracture failure exhibited a relatively large drift upon failure, while those failing due to bar bond slip showed smaller drift. Factors contributing to wall drift included horizontal slip, rocking displacement, cantilever bending deformation, and compressive settlement. The ultimate load increased by 71% as the embedded length increased from 75 mm to 175 mm, and it increased by 50% as the sleeve diameter decreased from 75 mm to 50 mm. The sleeves' performance was evaluated for feasibility based on the strength ratio, drift ratio, ductility ratio, failure mode, performance ratio, serviceability ratio, and length ratio. Only THS-8 met all the criteria, suggesting that the bar's embedded length should be at least 11 times the bar diameter.

A New Moment-Resisting Glulam Beam-End Connection Utilizing Mechanically Fastened Steel Rods—An Experimental Study

A new moment-resisting mass timber connection was designed based on the principles of force equilibrium in applied mechanics. The connection configuration utilizing two mechanically fastened threaded steel rods embedded into the end of a glulam beam section was experimentally investigated in this study. A gradually increasing transverse load was applied to the free end of a cantilevered beam, causing a bending moment on the beam-end connection until failure. Four different connection configurations were examined, each replicated twice to verify results. The beam connection parameters investigated were rod anchorage length (200 and 250 mm) and square washer size (38.1 and 50.8 mm). Test results show that increasing the washer size increased the connection bending strength by increments more significantly than those due to increasing the rod anchorage length. However, the connection configurations with the smaller-size washer, which failed mainly due to wood crushing under the washer, had higher ductility ratios than those with the larger-size washer, which failed due to steel rod yielding. In a real-life scenario, a structural element such as a glulam beam is usually loaded to approximately 50% to 70% of its design capacity, considering a reasonable margin of safety. The study estimates a maximum possible bending moment utilization factor for the strongest connection configuration that ranged between 34% and 48% compared to the maximum moment resistance of a supported glulam beam spanning an average length of 4.0 m to 6.0 m (a common span length in framed timber buildings) and has a cross-section size same as the one utilized in this study. This utilization factor is quite large for a timber connection, and thus, confirms a considerable moment-resisting capability of the new configuration developed in this study.

Experimental investigation of retrofitting seismically damaged reinforced-concrete frames using steel jacketing

Retrofitting seismically damaged structures provides significant economic and social benefits. To investigate the rationality of using steel jacketing to retrofit seismically damaged reinforced concrete (RC) structures, we initially tested a half-scale single-span two-story frame structure under pseudo-static loads to achieve a severe damage state. Subsequently, the structure was retrofitted using steel jacketing and tested under another round of pseudo-static loads. The seismic performances of the original and retrofitted structures were compared. The test results indicated that both the original and retrofitted specimens sequentially developed plastic hinges at the beam ends and the bottom of the columns, indicating a generally similar damage evolution mode. Comparing to the original structure, the retrofitted specimen exhibited an increase of 33% and 78.5% in initial stiffness and strength, respectively. Although the ductility ratio of the retrofitted specimen was reduced by about 14%, the ultimate drift ratios of both specimens exceeded the threshold value (1/50), indicating an adequate deformation capacity. The retrofitted specimen exhibited a certain degree of pinching behavior on the hysteretic curve because of the presence of extensive inclined shear cracks at the mid span of the beams and the progressive failure of the anchoring of the strengthening steel angle at the beam ends and column base. Consequently, the energy-dissipation coefficients of the retrofitted specimen were lower than those of the original specimen. Based on the test, the finite element analysis modeling method for RC frame structures retrofitted using steel jacketing was also studied. By comparing the numerical simulation analysis results with the experimental ones, the reliability of the proposed numerical simulation method was verified. This study can serve as a foundation for the practical application of steel jacketing to retrofit seismically damaged RC structures.

Seismic performance of light wood shear wall infilled timber frame structures with openings

To study the seismic performance of wood frame structures filled with light wood shear walls, three full-size single-layer single span wooden frame structures with infill walls were designed and manufactured. The beams and columns were connected by mortise-tenon joints, and quasi-static tests were conducted on the specimens under reversed cyclic load. The failure modes and load-displacement hysteresis performance of structures with door opening infill wall, window opening infill wall, and solid infill wall were investigated. The seismic performance was analyzed using indicators such as strength, ductility, and equivalent viscous damping ratio. The failure modes of light wood frame filling walls were the tearing of sheathing panel and the failure of nail connections. The filled wall with the opening initially exhibited inclined cracks at the corner of the opening, and then they extended to the periphery. Compared with the solid filled wall, the positive and negative bearing capacity of the structure with door opening decreased, and that of the structure with window opening decreased also. Because the specimens with opening in the filled wall were more conducive to the deformation of the structure when the bearing capacity was not significantly reduced, the ductility of the specimen with door opening was the highest.

Experimental Study on Hysteretic Performance of Steel Moment Connection with Buckling-Restrained Dog-Bone Beam Sections

Steel beam–column connections with dog-bone beam sections have gained significant attention and have been extensively applied. This is attributed to their ability to effectively centralize and integrate plastic hinges, thereby diverting potential damage away from the beam ends during earthquake events. In order to achieve the enhancement of the ductility and energy dissipation of connections by inhibiting local buckling during an earthquake event, a novel steel moment connection with buckling-restrained dog-bone beam sections was proposed in this paper. There were three types of proposed connections according to the different arrangements of restrained steel plates, including arranging the restrained plates only on the flanges, only on the web, and on both the flanges and webs of the dog-bone beam sections. In this study, three specimens with buckling-restrained dog-bone beam sections and one control specimen with a dog-bone beam section were tested under cyclic loading. The failure modes, hysteretic curves, skeleton curves, stiffness degradation ductilities, displacement ductility ratios, and energy dissipation capacities of the specimens were analyzed based on the experimental results to evaluate the seismic behavior of the proposed connections. The results indicated that the local buckling of the proposed connections was significantly reduced compared with the traditional connection with a dog-bone beam section under the condition of keeping the plastic hinges away from the beam–column connection core. The arrangement of the restrained plates in the dog-bone beam section had little effect on the bearing capacity and the initial stiffness, with errors all being within 6%. It is worth mentioning that the connection with restrained plates only on the flanges in the dog-bone beam sections showed a more obvious improvement in the deformation capacity and energy dissipation capacity of the connection, which increased by 21% and 16%, respectively. Additionally, high-quality welding between the beam and column, smooth cutting shapes on the weakened flanges, and the high-quality drilling of long slots at the fixed point in the restrained plates and the dog-bone beam sections should be guaranteed to improve the hysteretic stabilities of the proposed connections.

Overcoming the strength-ductility tradeoff of a 3D-printed Al-Si alloy by equal channel angular pressing

The integration of additive manufacturing and severe plastic deformation has produced an Al-Si alloy with superior mechanical properties. The novel processing pathway effectively avoids strength-ductility trade-off, resulting in an elongation increase of three times while maintaining a comparable yield strength to that of the original condition. The implementation of an intermediate annealing heat treatment (HT) before the subsequent equal channel angular pressing (ECAP) processing resulted in the most favorable combinations of strength and ductility. The ECAP process transformed the ultrafine interconnected eutectic network into ultrafine particles. This process also led to the formation of a heterogeneous grain size and the transformation of the 3-dimensional network of aluminides (Al2Cu) and Si-enriched precipitates into particles with varying sizes, ranging from 4 nm to 500 nm. In contrast, the ECAP processing without an intermediate annealing heat treatment led to a maximum yield strength increment of 22%. Notably, this enhancement in strength was achieved while preserving comparable levels of elongation to those observed in the as-built material. Hence, achieving the optimal combination of yield strength and ductility ratio demands a careful balance between various strengthening mechanisms, including subgrains and precipitates.

Lateral hysteretic behavior of precast concrete shear walls with unjointed vertical distribution bars and opening

Precast concrete shear walls with unjointed vertical distribution bars have desirable lateral resistance compared with cast in situ concrete shear walls and much less construction cost as no sleeve splicing joint is needed. However, the influence of opening in the precast panels on their lateral hysteretic behavior has not been fully investigated. This study presents the results of cyclic loading tests of three full size precast concrete shear walls with unjointed vertical bars and opening. The test results showed that these shear walls had similar failure modes as a cast in situ concrete shear wall, such as cracking in the corners of the opening and the concrete and steel bars crushing at the bottom corners of the shear walls. The peak load of the positive and negative loading cycles and the stiffness of the unjointed shear wall with a window opening were 14.6%, 4.3% and 1.3%, respectively, smaller and the ductility ratio was 37.6% higher, than an otherwise the same cast in situ shear wall. The lateral stiffness of the unjointed shear wall with a door opening was 35% smaller than that of the one with a window opening, due to the stiffness contribution of the wall segment underneath the window opening. The development of the longitudinal strains of concrete and steel strain along the height of the wall limbs generally met the plane section assumption. However, those next to the vertical joint interface were affected by the development length of the shear force after the bedding mortar cracked under tension. The determination of the development length needs to consider the influence of the stiffness of the link beam and the wall segment underneath the opening.

Multi-scale microstructure manipulation of an additively manufactured CoCrNi medium entropy alloy for superior mechanical properties and tunable mechanical anisotropy

Laser beam powder bed fusion (PBF-LB) additive manufacturing (AM) technology has become a versatile tool for producing new microstructures in metal components, offering novel mechanical properties for different applications. In this work, enhanced ductility (∼55% elongation) and tunable mechanical anisotropy (ratio of ductility along vertical to horizontal orientation from ∼0.2 to ∼1) were achieved for a CoCrNi medium entropy alloy (MEA) by multi-scale synergistic microstructure manipulation (i.e., melt pool boundary, grain morphology and crystallographic texture) through adjusting key PBF-LB processing parameters (e.g., laser power and scan speed). By increasing the volumetric energy density (VED) from 68.3 to 144 J/mm3, the melt pool size enlarges, and the crystallographic texture transitions from <100>//BD to <110>//BD due to the maximum thermal flux direction changing for different melt pool dimensions, which affects the proportion of grains that have different growth directions. Moreover, excellent mechanical properties of 890 MPa ultimate tensile strength and ∼55% elongation to failure can be achieved for loading perpendicular to the build direction with only a ∼15% reduction in properties for loading along the build direction. The superior combination of mechanical properties is achieved by processing parameter-controlled strengthening of melt pool boundary interfaces, heterogeneous deformation induced strengthening through bimodal grain structures, and favorable grain orientation for dislocation slip and twinning formation, which was significantly more activated in the <110>//BD texture than in the <100>//BD. This study offers new insights into achieving multi-scale synergistic microstructure manipulation via PBF-LB for desired strength, ductility, and mechanical anisotropy in a CoCrNi MEA.

WITHDRAWN: Out-of-plane push-over testing of masonry wall reinforced with prestressed wedges

Masonry partition walls are vulnerable to lateral loads, including seismic, wind, and concentrated push loads. Various strengthening metal fittings have been proposed to improve lateral load resistance, particularly against seismic loads. This study introduces the use of prestressed wedges as a novel reinforcement method for masonry partition walls to enhance lateral load resistance. The resistance of the masonry partition wall against lateral-concentrated push loads was assessed using an out-of-plane push-over test on specimens sized 2300 × 2410 × 190 mm3. The presence or absence of wedges and wedge spacing were set as variables. The push-over test results showed that both the unreinforced specimen and the specimen reinforced with 300 mm spaced wedges toppled, while the specimen reinforced with 100 mm spaced wedges remained upright. Peak loads were measured to be 0.74, 29.77, and 5.88 kN for unreinforced specimens and specimens reinforced with 100 mm and 300 mm spaced wedges, respectively. Notably, a tighter reinforcement spacing yielded a similar strength, as expected, which was attributed to the increased friction force between the masonry wall and steel frame. The W-series specimens exhibited a trend comparable to that of the displacement ductility ratio. Overall, the findings validate that prestressed wedges improve the out-of-plane strength of masonry partition walls.

Experimental Study on Seismic Performance of Partially Corroded Squat RC Shear Walls in Coastal Environment

In coastal environments, squat reinforced concrete (RC) shear walls are susceptible to local accumulation of moisture and chloride salts, causing local corrosion in the shear walls, which in turn affects their seismic performance. Four squat RC shear wall specimens were designed considering the corrosion locations and the heights of the corroded area. The seismic performance of partially corroded squat RC shear wall specimens was analyzed through a quasi-static test. The results show that as the height of the corroded area increases from 15% to 25% of the total height, the area of the hysteresis loop of the shear walls obviously decreases. As the height of the corroded area increases from 0 to 15% and 25% of the total height, the peak and ultimate displacements of shear walls are, respectively, reduced by 6.7% and 19.2% in the positive loading direction, and are, respectively, reduced by 22.3% and 18.3% in the negative loading direction. Compared with the unilateral corroded shear wall, the area of the hysteresis loop and the stiffness of the bilateral corroded shear wall remain approximately unchanged, and the peak and ultimate displacements, the shear strain, and the ratio of shear deformation to horizontal displacement are reduced. Compared with the uncorroded shear wall, the hysteresis loop of the unilateral corroded shear wall is plump, the displacement ductility ratio and the plastic rotation angle are both increased, and the stiffness degradation is relatively slow.

Retrofitting of squat RC column by using TRM strip under axial load

This study investigates the retrofitting of reinforced concrete columns with TRM strips. Seventeen test specimens were produced, and one was chosen as a reference test specimen. Damaged by loading up to 50% of their maximum axial load-carrying capacity test specimens were retrofitted with two different carbon textiles. In addition to the textile type, TRM strip width, strip spacing, and the use of anchors were determined as experimental variables. Maximum bearing capacity, displacement at bearing capacity, initial stiffness, displacement ductility ratio, and energy consumption capacity were calculated using the axial load-displacement graphs obtained from the experimental study. Depending on the obtained results, the effects of experimental variables on the behavior of damaged reinforced concrete columns were interpreted and compared. It has been determined that the retrofitting method presents very successful results. It has been observed that the fan-type anchor, which is rarely used in literature studies, significantly increases the maximum bearing capacity and energy consumption capacity values of test specimens. Finally, the experimental results were compared with those obtained from the numerical models created by the ABAQUS finite element software.

Determining the optimal layout of energy-dissipating mechanisms for hybrid self-centering walls

To eliminate the inherent energy dissipation deficiency of self-centering walls, hybrid self-centering walls (HSWs) have been developed by employing internal or external energy dissipating (ED) mechanisms. Mild steel bars have been extensively used as energy dissipators among ED mechanisms due to their affordability and simplicity. This study investigated the effect of ED bars layout on the damage, response features, collapse probability and collapse risk of HSWs. To this end, five different layout scenarios were defined first, and their response was studied by developing numerical models. Conducting nonlinear static and dynamic analyses (IDA), the scenarios damage, response features, collapse probability and risk were estimated and further examined to determine the optimal ED bars layout. Fragility analysis was performed on global and local scales, using IDA results, to estimate scenarios collapse probability. The results revealed that the wall with ED bars at the boundary elements outperformed other scenarios. Placing ED bars at the boundary elements of HSWs decreases the self-centering capability, fundamental period, collapse probability and the extent and severity of damage (especially in toe regions), while increases the energy dissipation capacity, adjusted collapse margin ratio and structural demand. Increasing ED bars cross-sectional area increases the extent and severity of damage. Using IDA results, the wall with ED bars at the boundary elements achieved the lowest ductility ratio; moreover, the response modification factor 3 was recommended for the strength-based design of HSWs. An optimality index (OI) was proposed herein to interpret the results quantitatively and determine the optimal layout. The calculated OI showed that placing ED bars at the boundary elements or along the wall width can be considered the optimal ED bars layout for achieving better seismic performance and decreasing the collapse probability and seismic risk of HSWs.

Regression algorithms-driven mechanical properties prediction of angle bracket connection on cross-laminated timber structures

The construction of structures using cross-laminated timber (CLT) has grown in popularity as a result of its environmentally friendly and high-strength characteristics. The primary function of angle bracket connections is to resist the force of CLT structures under horizontal forces, which is essential to ensure the seismic resilience and ductility of CLT structures. A regression algorithms-driven method for predicting the mechanical performance of angle bracket connections is introduced in this study. As input parameters, the geometric dimensions of the angle bracket connector, the connection method of the connector with the wall and floor slabs, and the properties of the CLT panel are utilized to predict the yield load, the maximal load, the initial stiffness, and the ductility ratio of the angle bracket connection. Prediction models were developed using the collected data from 110 angle bracket experiments, and each prediction model's performance was discussed in depth. Lastly, the permutation importance and SHapley Additive exPlanations (SHAP) value analysis were used to interpret the prediction models. The results showed that the extreme gradient boosting (XGB) algorithm could accurately predict the maximum and yielding load of the angle bracket connection, with R2 reaching 0.968 and 0.939. Furthermore, in predicting the initial stiffness of the angle bracket, the XGB algorithm performed the best with an average ratio of predicted to actual values of 0.985. The results indicated that this study proposed an accurate and efficient method for angle bracket connection to predicting its mechanical properties and confirmed the trustworthiness and feasibility of the prediction models.

Uniform deformation distribution of structures at different seismic hazard levels using endurance time method

This paper evaluates the application of the endurance time method in the optimum performance design of structures using the uniform deformation theory. The structures used in this study include shear-building systems with 5, 10, and 15 stories, and steel moment-resisting frames with 3, 7, and 12 stories. Initially, shear-building systems are optimized to have uniform story ductility ratios at low, moderate and high seismic hazard levels separately using three sets of ground motion records and a compatible series of endurance time acceleration functions. The effectiveness and accuracy of the endurance time method are assessed by comparing lateral force distribution obtained from this method with its corresponding attained from ground motion records. Moreover, as the number of stories and target ductility increases, the compatibility of these two methods improves. However, it is found that the optimum structure at one seismic hazard level does not necessarily lead to the optimum structure at other seismic hazard levels. Next, by adding dampers with gap to the systems, a procedure is suggested to optimize these structures at different seismic hazard levels simultaneously. These dampers are activated at moderate and high seismic hazard levels. Finally, similar optimization algorithm is used for steel moment-resisting frames to make their story drift ratios or plastic hinge rotations uniform along the height at different seismic hazard levels. Results show that combining endurance time method and uniform deformation theory leads to a promising optimization procedure that can significantly reduce computational costs with reasonable error.

Experimental study on out-of-plane seismic performance of precast composite sidewalls of utility tunnel with grouting-sleeve joints

The precast composite reinforced concrete wall with the advantages of fewer joints, superior impermeability and rapid construction provides an efficient and environmental friendly alternative in the construction of underground utility tunnels in the last few years. To investigate the seismic performance of precast concrete composite walls of utility tunnels with grouting-sleeve connection under out-of-plane loads, a series of quasi-static cyclic tests were performed on the full-scale sidewall specimens with different axial compression ratios in this study. The experimental results including the failure modes, crack distributions, and the influence of different connections on the out-of-plane seismic performance of precast concrete composite wall were carefully examined and compared with those from the cyclic tests of the cast-in-place sidewalls of the utility tunnel. The test results show that the seismic performance of the precast concrete composite sidewall specimen, such as the hysteresis curves, the ultimate bearing capacity, stiffness degradation pattern and the ductility ratio, is basically the same as that of the cast-in-place specimen, indicating that the seismic performance of the prefabricated structure is equivalent to that of the cast-in-place structure. Moreover, the grouting-sleeves of the joints can effectively transfer the reinforcement stress until the failure of the precast concrete composite sidewall specimens, which exhibits excellent out-of-plane ductility and serviceability.

Seismic Performance Evaluation of Reinforced Concrete Buildings Retrofitted with a New Concrete Filled Tube Composite Strengthening System

This study proposes a concrete-filled tube composite strengthening system (CCSS), which is a new concept that can improve and supplement the vulnerability of existing CFT seismic strengthening methods. The CCSS seismic reinforcement method is easy to construct and integrates with the existing frame and reinforcement. It is one of the seismic strengthening methods that allows the simple calculation of the required amount of seismic reinforcement and can efficiently increase the strength when applied to existing reinforced concrete (R/C) buildings with non-seismic details dominated by shear failure. To examine the seismic safety of the proposed CCSS, two framework specimens were prepared based on an existing R/C building with non-seismic details. A pseudo-dynamic test was conducted on the unreinforced framework specimen and the framework specimen reinforced with CCSS to verify the seismic strengthening effect of applying CCSS to the existing R/C framework, i.e., in terms of the load–displacement characteristics and seismic response control capability. Based on the pseudo-dynamic test results, restoration of the force characteristics was proposed for the nonlinear dynamic analysis of the building reinforced with CCSS. Nonlinear dynamic analysis was conducted based on the proposed restoration of the force characteristics, and the results were compared with the pseudo-dynamic test results. Finally, for the commercialization of CCSS, nonlinear dynamic analysis was conducted on the existing whole R/C building with non-seismic details that was reinforced with CCSS. The seismic strengthening effect was then verified by examining the seismic response load, displacement characteristics, and the degree of seismic damage to the members based on the ductility ratio before and after seismic strengthening. The study results show that under a design basis earthquake with a magnitude of 200 cm/s2, the unreinforced R/C building exhibits shear failure, and light seismic damage is expected on the CCSS-reinforced building.

Investigating seismic behaviour of cold-formed steel moment frames with the welded through-plate flexural connection

The Cold-Formed Steel (CFS) construction in seismic regions requires carefully selecting and designing an approved seismic-force resisting system. Among the available seismically-resistant structural systems, the bolted CFS moment frames have recently gained some attention. However, given the currently existing design issues associated with the bolted connections in CFS moment frames, this paper seeks to conduct a numerical investigation into the potential substitution of bolt fasteners with the weld materials in CFS frames. The objective is to explore the possibility of including the welded connection as an alternative to bolted connections in subsequent editions of the ASCE 7 code. To this end, finite element models, consisting of two built-up CFS beams and twenty-three flare-bevel-groove and fillet weld specimens, are initially validated against the cyclically and monotonically loaded tests with data available in the relevant literature. Subsequently, the verified weld and CFS beam models are incorporated in the simulation of thirty-four CFS beam-to-column welded moment connections, each differing in beam dimension, weld length and size, and gusset plate thickness. The built-up beams comprise back-to-back and lip-to-lip double C-section profiles. Stress variations along the weld lines, derived initially from nonlinear finite element analyses and then computed from the theoretical elastic analysis, are compared to establish a basis for categorizing stress distribution patterns in the longitudinal welds. Finally, six CFS frames assembled with the welded moment connection and subjected to a combined column axial compression and cyclic lateral drift are examined, resulting in an estimated seismic modification coefficient, R, equal to 3.8. Overall, the welded moment connections demonstrate a stable seismic response with an average ductility ratio, μ, of 2.7. The dominant failure mode is a locally developed ductile fracture in the two end segments of the longitudinal welds, identified as critical regions.

Experimental and numerical investigation of large-scale reinforced concrete deep beams designed with the Generative Tie Method

This study presents a comprehensive evaluation of the behavior of two large-scale reinforced concrete deep beams designed using the Generative Tie Method (GTM). Different admissible values of the loss of compressive strength in the concrete (ηadm) were considered, and the results were compared to a deep beam designed with the help of the Strut-and-Tie Method (STM). The study highlights the importance of selecting an appropriate ηadm value for designing reinforced concrete deep beams capable of exhibiting ductile behavior using the GTM. The results show that specimen SIIIa, designed using the GTM with a ηadm of 0.5, demonstrated a highly optimized reinforcement layout with the most pronounced reinforcement yielding, indicating ductile behavior. Among the studied specimens, the one designed using GTM with an ηadm of 0.7 exhibited the lowest maximum crack width and the highest ultimate load despite demonstrating brittle failure. Both GTM-designed specimens demonstrated maximized material efficiency and higher ductility ratios than the deep beam designed using STM. By integrating the bond-slip model proposed in the fib Model Code 2010 into the finite element analysis framework, the numerical simulations produced highly accurate predictions of the behavior of the deep beams. The authors suggest further investigations to enhance the proposed numerical strategy and apply the GTM for designing reinforced concrete deep beams with organic or optimized shapes.