Concrete Connections Research Articles

Precast concrete wall-raft connectors for increasing the lateral load capacity: An experimental and analytical approach

Precast structural walls and rafts commonly resist lateral load in structures owing to improved traits and faster construction. The behavior of five different types of precast reinforced concrete structural wall and raft connection systems is evaluated in this study. In all five configurations, the cyclic load is applied in the wall systems to observe the lateral load-carrying capacity and hysteretic characteristics. The damage and failure patterns were assessed. To confirm and contrast the behavior of the proposed precast structural wall and raft connection systems with the experimental findings, FEM analysis was used. Only shear and flexural cracks were observed. The specimen with 12 mm dia rods has the maximum load carrying capacity of 10.23 kN in the negative cycle, which is 57% more than the specimen without grouting and connector. The suggested connection can improve the resistance behavior in all key directions by absorbing more energy than precast walls under dynamic load.

An Explicit Approach for Determining the Rational Length of Steel Portion in Steel–Concrete Hybrid Girder Bridges

The steel–concrete hybrid girder bridge structure is a combination of steel and concrete members in the direction of the bridge length. In long-span segmental concrete box girder bridges, the utilization of lightweight steel girders in the middle portion of the main span would greatly reduce the bridge self-weight while decreasing concrete creep and shrinkage effects. A critical parameter in the design of hybrid girder bridges is the rational length of the steel portion as a part of the main span (in other words, the rational location of the steel–concrete connection). Based on the concept of system equivalence, the steel–concrete hybrid system is equivalent to a full-concrete system with a reasonable span arrangement. The governing condition of the equivalence is that both systems have the same magnitude of self-weight hogging bending moments over the piers. Applying the system equivalence method, the rational length ratio of the steel portion to the main span (ξ) is explicitly solved, and its relationship with the length ratio of side span to main span (λ) is established. Finally, the proposed analytical approach is validated by five case studies, indicating that it is an effective and efficient method for the preliminary design of hybrid girder bridges.

Assessment of the degradation state of joints in large-panel buildings

Large-panel buildings have been in continuous use for several decades, making it necessary to inspect and assess the technical condition of the structures. This paper presents a research problem for investigating the quality of prefabricated elements connections and the effect of degradation on their load-bearing capacity. Visual, non-destructive and destructive methods were used to test concrete and steel connections. Conclusions were formulated on the suitability of the various test methods for investigating joints. Based on the results obtained, a computational analysis of the effect of selected degradations on the load-bearing capacity of the joints was performed. The calculations indicated that the ultimate limit states can be exceeded in the case of carelessly made connections. This means that hidden reserves of load-bearing capacity can be exhausted due to progressive degradation processes, material ageing or the occurrence of exceptional loads. Therefore, it is reasonable to carry out condition evaluations of joints on the basis of numerical calculations that take into account the actual strength characteristics and material discontinuities.

Seismic behavior of concrete columns with ends transformed via perforated H-shaped steel and engineered cementitious composite

A novel structural detail is proposed to strengthen or shift the plastic hinge regions of concrete column-footing connections by using perforated H-shaped steel and engineered cementitious composites (ECC) in this study. Two transformed concrete columns and a normal concrete column were tested under a constant axial load and quasi-static reversed cyclic load to explore their seismically important features, including failure modes, hysteretic response, energy dissipation, stiffness degradation, and strain. Furthermore, a numerical study was also conducted to investigate the influences of critical parameters on seismic performance, and a formula for predicting the shear capacity of concrete columns is proposed. The results reveal that the seismic performance of concrete columns can be improved by embedding perforated H-shaped steel and using ECC at each end, and the plastic hinge can be relocated away from the column ends. The finite-element results agreed well with the experimental results. A high shear-span ratio adversely affects the seismic performance of the transformed concrete columns. An increase in the axial load ratios and H-steel insertion depth can enhance the load-carrying capacity of the models.

PELAKSANAAN PEKERJAAN PLAT LANTAI DENGAN BETON PRECAST PADA PROYEK PENATAAN GGM TAHAP 1

Abstract
 The building structure is one of the most important elements in a building construction. So the selection of the right implementation method is very important to be able to get the best and maximum results. Replacing conventional methods to become more modern is one of the efforts that can be done by managers. As in the implementation of the skywalk work, it also uses a more modern method, namely by applying a precast concrete system to the floor slab.
 The purpose of this study: (1) to know and understand how to carry out the work of preparing/installing precast concrete floor slabs. (2) knowing and understanding how to carry out precast concrete connection work. From this it will be known the method of implementation, the stages of implementation carried out, the specifications of the precast concrete used, as well as the types and specifications of the heavy equipment used.The results of this study are: the implementation stage starting from the mobilization of materials, preparation work, HCS work and the last stage is the connection stage. The precast used are: Width 1,200 mm, Length 3,720 mm, Weight 932.14 kg. The iron used in the connection is D10 in size.
 Keywords: Precast concrete, Implementation Method, floor slab

Progressive collapse resistance of reinforced concrete beam-column connection under fire conditions

To reveal the reinforced concrete (RC) structural response under fire-induced progressive collapse scenarios, 3D finite element (FE) models were developed to investigate the effect of high temperatures on the collapse resisting mechanisms of RC beam-column connections. To describe the behavior of RC connections at elevated temperatures, temperature-dependent thermal and mechanical properties of concrete and reinforcing steel were adopted in the 3D FE model. The sequentially coupled thermal–mechanical analysis was performed with the explicit solver in a quasi-static manner. The concrete damaged plasticity (CDP) and ductile damage for metals (DDM) were adopted to better describe the failure of concrete and steel rebar, respectively. The proposed numerical model was validated by experimental data at different temperatures from literature. To understand better the collapse resistance of RC beam-column connections, a new loading scheme was adopted in the developed model. The load capacity of RC connection under fire conditions was investigated analytically and numerically. The effects of top and bottom reinforcement ratios, concrete strength, beam depth and fire severity on the collapse resisting mechanisms were investigated. The regulated chord rotation failure criteria recommended by the U.S. Department of Defense (DoD) were utilized and showed to be conservative on the collapse identification of RC structures under fire conditions.

Single-side yielding precast concrete slotted beam-column connection with replaceable energy dissipation bars: Experimental investigation and finite element analysis

A new type of rebar coupler, non-slipping combined threaded sleeve (NCTS), is proposed, and based on this, replaceable energy dissipation (ED) connector is assembled. An innovative single-side yielding slotted beam-column connection with replaceable ED bars (SYSC-REDB) was developed by placing the ED connector in the beam end bottom of prefabricated concrete frame. Four quasi-static tests were conducted to evaluate the seismic behavior, such as the damage distribution, failure characteristics, hysteretic response, ED capacity, and deformation pattern. The hysteretic curves were stable and full without pinching, indicating excellent seismic performance. The deformation pattern of single-side yielding can enhance the ED capacity of connectors, concentrate damage and failure on the ED bars, and significantly reduce the deformation of the top beam and beam elongation. The joint could be repaired by replacing the ED bars via the inner space of the NCTS. The seismic behavior of the repaired specimens was similar to those of the original specimens. In addition, the finite element models of ED connector and SYSC-REDB joint were established by ABAQUS respectively, and their accuracy were verified by comparing with the test phenomena and results. Furthermore, parametric finite element analysis was executed for some key factors, including the top-hinge area depth, ED bar area, and top longitudinal reinforcement bar area. Theoretical and parametric study of bending moment capacity is also performed.

Punching shear behavior of reinforced concrete flat slab column connection containing recycled eggshell powder

Every day, millions of bio-waste eggshells are discarded in the environment by poultry farms, homeowners, bakeries, and the food industry around the world. The possibility of recycling eggshells as a cement replacement in concrete may solve the disposal issue of eggshells. Also, cement production causes the release of carbon dioxide, which contributes to global warming. Replacing cement with eggshell powder (ESP) reduces the level of cement production and indirectly decreases carbon dioxide emissions into the atmosphere. This paper aims to investigate the structural effect of the ESP content as a cement replacement on the punching shear behavior of reinforced concrete (RC) flat slab column connections. The possibility of ESP reuse in RC flat slab structures tested for punching shear was investigated. Four well instrumented RC flat slab column connections (S1, S2, S3, and S4) were cast using four different concrete mixtures containing 0, 5, 10, and 15% ESP, respectively. The slab panels (620x620x50) mm with a constant square column size of (100x100) mm were simply supported and tested under concentrated column load. The test results of different concrete mixes made with ESP content are reported. The test results of RC flat slab behaviors, including failure mode, load–deflection response, load-corner rise, load–strain curves, load-edge rotation response, punching perimeter, angle of punching, shear load, ductility, and stiffness of tested slab panels with and without ESP are discussed. The experimental punching shear load and punching perimeter were compared with those obtained by code model equations in ACI, BS, and Eurocode. It can be concluded that the experimental shear load and stiffness for the slab containing 10% ESP content increased by 5.85% and 24% than that of the control slab without ESP. Eggshell powder could be applied to a certain extent to replace cement in the RC flat slabs.

A finite element study on the ultimate lateral drift capacity of interior reinforced concrete flat slab-column connections

Reinforced concrete (RC) flat slabs may be a part of the lateral load resisting system or may only serve as a gravity load bearing element in RC structures. In both cases, RC slab-column connections have a crucial role in the global seismic performance of RC buildings. Punching shear failure in flat slabs concentrated in the slab-column connection region is a common brittle failure mode which can adversely affect the global seismic behavior of structures. However, few studies have been done on the numerical simulation of brittle shear failure in slab-column connections under simultaneous gravity and lateral loads. In this paper, to evaluate the behavior of RC slab-column connections under simultaneous gravity and lateral loads and to examine the effects of various influential parameters on the lateral drift capacity of the connections, a numerical study is conducted on interior slab-column connections. The investigated influential variables are the flexural reinforcement in the slab, slab thickness, and the dimensions of the supporting column. The numerical study is implemented in the finite element software ABAQUS. First, the numerical model is verified through modeling three interior RC slab-column connections tested in other experimental studies. Then, all the connections are analyzed under the simultaneous effects of gravity and lateral loads and their lateral load-drift curves are determined. According to the analysis results, in addition to the gravity load intensity, other variables such as flexural reinforcement ratio, slab thickness, and the size of the supporting column affect the lateral behavior of the connection.

Lem Beton Pengaruh Penggunan Lem Beton Pada Sambungan Pengecoran Antara Beton Lama dan Baru

In carrying out concrete work, if the casting work is not completed, then the casting must be stopped at places that do not endanger the construction according to the instructions of experts in accordance with the plan drawings. Casting of joints between old and new concrete with an overview of inclination angles of 0⁰, 45⁰, and 90⁰. Joints are part of the concrete construction to provide a safe stop for the casting for the stage of construction. The casting is carried out in several steps, in the first step filling the concrete in the cylinder mold up to half of the total, after the concrete has reached the age of 7 days, then the next concrete as connection concrete fills half of the old concrete by coating the old concrete connection using glue which is a mixture of additon addibond glue + water and without concrete only a mixture of cement + water. This research was conducted so that the implementation in the field knows the function of each slope angle at 0⁰ is used in casting column connections, 45⁰ is carried out on casting plate and beam connections, and 90⁰ is carried out on casting pile cap foundation connections. The test results of the compressive strenght & split tensile strength of concrete showed that the variation of the joint slope using glue was greater than the variation of the connection without. For the results of the greatest compressive strength test in intact concrete with an average strength value of 35,29 Mpa, while in the split tensile strength test the concrete got an average strength value of 2,37 Mpa.

Seismic Performance of Precast Concrete Frame Beam-Column Connections with High-Strength Bars.

As the construction industry is striding towards the industrialization of green buildings, a precast concrete frame beam-column joint with high-strength reinforcement was proposed. Simulate reversed cyclic loading was carried out on two precast connections and one cast-in-place connection to examine the seismic behavior of the proposed new precast connection. The main test variables between the two precast connections were the strength of the reinforcement at the bottom of the beam. The failure shape, hysteresis curve, skeleton curve, strength, deformation ability, stiffness degradation, and energy dissipation were monitored and compared with the cast-in-place connection. The findings of this paper showed that the precast joints had good strength reserve, and the seismic performance in the later stage of loading even exceeds the cast-in-place joints. It was also found that the plastic hinge zone of the beam could be moved away from the column surface via reinforcement method. Additionally, based on the experiment, a detailed nonlinear finite element analysis (FEA) method was developed to reproduce the test response of specific types of bending moment-resistant precast concrete beam-column connections under a reversed loading test, which provided a theoretical reference for further research of the connections.

Experimental Study on Seismic Behavior of Precast Bolt-Connected Steel-Members End-Embedded Concrete (PBSEC) Beam-Column Connections

With the rapid development and research of precast concrete frame structures, it is not difficult to find that the structural form and seismic performance of dry-connected precast joints have always been the focus of research. Since this type of structural system is complex, the construction is inconvenient in practical application, and many additional parts need to be installed, this paper develops a kind of precast bolt-connected steel-members end-embedded concrete (PBSEC) beam-column connection to solve the shortcomings of the current dry-connected precast joints. There is no wet work in the assembly process, and all-dry construction and assembly methods are used. There is no need to pour concrete and support formwork, which significantly improves construction efficiency compared to wet and cast-in-situ connections. Low cyclic reversed loading tests were conducted to obtain test data, such as failure mode, hysteresis curve, skeleton curve, stiffness, ductility, and deformation capacity of the precast concrete joint. The failure mode of the PBSEC joints is the buckling failure of the connecting steel plate, leading to a perfect seismic capacity and collapse resistance of the structure. The hysteresis curves of the PBSEC joints are bow-shaped and full in shape, showing high energy dissipation capacity. The bearing capacity of the joints begins to rise rapidly at the initial loading stage and then decreases slowly after reaching the peak, which is an ideal shape. By summarizing the average peak load, strength degradation coefficient, loop energy per cycle, loop energy per level, and cumulative energy damping coefficient, it is found that the joint using 10 mm thick Q235 steel can obtain the most suitable failure mode and obtain the best energy dissipation performance. When the strength of the steel plate material increases, the energy dissipation performance of the joint drops.

Rouzhi 柔知 “the Supple Way of Knowing”: Cognitive Traps and Embodied Intellectual Virtues

Abstract This essay explores the epistemological implications of the Daoist concept of rou 柔 or “suppleness” and its related notion rouzhi 柔知 or the “supple way of knowing.” It is comprised of three interrelated parts. Part one starts with a brief introduction to rou and its usage in early Chinese texts, where it outlines three important ways to approach it. In part two, it moves to a careful reading of female Daoist Cao Wenyi’s 曹文逸 Lingyuan Dadaoge 《靈源大道歌》 (The Song of the Ultimate Source of Great Dao or Dadaoge for short), where it explores her text as formulating a Daoist way of knowing based on an appreciation of rou. The third section discusses concrete connections between rou and specific epistemic virtues.

Pullout Behavior of Anchored Steel Bars and Grouted Headed Bars

This paper aims to study the tensile behavior of several types of anchored steel bars used in the cast-in-place connections considering the bonding condition between steel bars and concrete and in the precast concrete connections based on the bond behavior of the headed steel bars grouted in ducts. The pullout tested bars have been experimentally conducted using a static tensile loading in order to evaluate the pullout behavior, the failure mode, and the required development length. Nine pullout tests have been conducted for the cast-in-place straight and 90-degree hooked steel bars, and the grouted headed bars. In addition, a comparison of the calculated development length has been introduced considering different building codes. Results have showed that the peak pullout load has been observed in the cast-in-place 90-degree hooked end bars. Furthermore, the pullout load and the required development length of the cast-in-place straight end and the grouted headed bars have been similar, and they have been higher than 97% of the cast-in-place 90-degree hooked end bar. For the grouted-headed bars and the cast-in-place 90-degree hooked, ACI 318-19 and ECP 203-2020 have showed more rational results compared to experiments while it has been very conservative for cast-in-place straight end bars.

Experiments on cyclic behaviour of cold-formed steel-rubberised concrete semi-rigid moment-resisting connections

This paper presents the results of full-scale physical tests on a recently developed cold-formed steel (CFS) semi-rigid moment-resisting connection infilled with rubberised concrete (RuC) for seismic application. The connection comprises side-plates attached to both sides of built-up tubular CFS beam and column sections through either screwed or welded connections. The tests were performed on both bare steel and CFS-RuC composite connections under cyclic loading for comparison purposes. The predominant modes of failure are beam local buckling and side plate plasticity in the bare steel connections and screw shear failure in the composite connections. The results show that the composite connection typically reaches 45% higher strength and 21% greater energy dissipation capacity than the bare steel connection both having 24 screw arrays. These indicate the beneficial effects of the infill RuC in prevention of the beam local buckling in connections with identical connection configuration. The energy dissipation capacity of the bare steel connection having 36 screw arrays, however, was 70% greater than that of the composite connection with 24 screw arrays. This reflects side plate plasticity being a more effective energy dissipation mechanism than the other identified mechanisms.

Learning to teach coding through argumentation

For computer science to be for all students, coding needs to be integrated within existing curricula for authentic and interdisciplinary computer science learning. The present study examined the use of transformative pedagogy of teaching coding through argumentation, specifically focusing on how teachers conceptualized teaching coding through argumentation. Fourteen elementary teachers learned coding and argumentation in a semester-long professional learning course. Participating teachers’ coding knowledge, views of coding, and beliefs about using argumentation in teaching coding were examined. A concurrent triangulation mixed methods design was used. Quantitative data included coding exams and surveys and qualitative data included interviews and course artifacts. Study findings include: (a) there were sustained groups with more complete coding knowledge and less complete coding knowledge throughout the semester, (b) coding was often viewed as a means to create another modality for other subject teaching with no difficulty of integration, (c) a few teachers articulated their beliefs about using argumentation in teaching coding with concrete relational connection to coding, and (d) teachers who consistently exhibited more complete coding knowledge conceptualized teaching coding with argumentation in more concrete ways.

Joint shear strength prediction of beam-column connections using machine learning via experimental results

Machine learning (ML) had already advanced rapidly in recent years, promising to completely change and enhance the function of data science in a spectrum of areas. This paper proposed a framework for predicting the shear strength of reinforced concrete beam-column connections subjected to cyclic loading. Six classical prediction models (Ordinary least Squares (OLS), Support Vector Machines (SVM), K-Nearest neighbour regression (KNN), Multivariate Adaptive Regression Splines (MARS), Artificial Neural Networks (ANN), and kernel regression with mixed data types (Kernel regression)) were proposed, and a total of 98 dataset results were collected and used to train and evaluate the suggested framework models. The most important factors influencing the joint shear strength were chosen based on the previous experimental results to create a parametric equation to forecast the joint shear strength. Also, the experimental joint shear strength was compared with that predicted using the proposed framework model and the parametric equation. The results show that the Kernel regression predicted the shear strength of beam-column connections subjected to cyclic loading with the highest accuracy. Moreover, the squared R-value is 0.9752 which reflects the high efficiency of the Kernel model between other models. The results also reveal that the joint shear strength predicted using the Kernel regression is closer to the experimental values than the joint shear strength predicted using the parametric equation. As a result, the proposed model may be a useful tool for researchers and reinforced concrete engineers in accurately estimating the joint shear strength of beam-column connections (i) within the ranges of values used in this study for the input data, and (ii) with less time and cost than constructing other numerical schemes.

Flexural behavior of prefabricated high-strength steel-concrete composite beams with steel block connectors

To study the flexural behavior of high-strength steel-precast concrete slab (HSS-PCS) composite beams with steel block shear connectors (SBSCs), seven HSS-PCS beam specimens subjected to a single concentrated load were tested, considering the parameters of concrete strength, steel strength, and shear connection degree. Through this experiment, the primary specimen information of vertical load, deflection, mid-span section strain, and interface slip were established. The HSS-PCS composite beam with steel block shear connectors has good overall working performance with high bending capacity and stiffness, and three failure modes are recorded including cracking at the tongue and groove joints, crushing of mid-span concrete slab, and failure of shear connections. The composite beams show a high degree of brittleness under these three failure modes, which should be considered in practical design. The existing design theory and standards are generally suitable for predicting the bending capacities of the novel prefabricated composite beams, in which the Eurocode 4 is slightly conservative, while the Chinese design specification has relatively good prediction results for the composite beams with partial shear connections.

Tensile and flexural tests on ultrahigh performance concrete grouted sleeve connection

AbstractConnections in the assembled precast elements become essential locations for creating structural continuity. However, the construction challenges of conventional steel sleeve connections, such as rebar embedment length, rebar congestion, and formed grout defects (i.e., voids), are still a concern area for researchers and engineers. In this study, a proposed ultrahigh performance concrete (UHPC) grouted sleeve connection was presented for assembled precast elements, which might reduce defects, enhance durability, and accelerate structure construction. The tensile test of grouted sleeve connection with different grouting materials, rebar diameters, and anchoring lengths was conducted to determine an optimal anchoring length used in the flexural design. The precast specimens with the UHPC grouted sleeve connection were tested under flexural load. Also, strain changes in concrete, sleeve, and rebar were reported in tensile and flexural tests. The tensile test results showed two types of failure modes, the rebar rupture and bond failure between rebar and grouting. The recommended rebar anchoring length in the flexural design was six times the rebar diameter. The flexural test results showed that the precast specimen with or without the shear key has a similar failure mode as compared to the cast‐in‐place specimen, while their average cracking load, yield load, and ultimate load were 27.9%, 11.0%, and 7.4%, respectively, which is less than those of the cast‐in‐place specimen. Also, the flexural cracking resistance was the highest in the sleeve segment, followed by the joint region and the rebar segment. This study provides a reference for the design of the UHPC grouted sleeve connection for assembled precast elements.

Experimental Study on Seismic Performance of Prefabricated Frame Column Joints with a High Axial Compression Ratio

A new type of an assembled monolithic concrete column encased by partial outsourcing steel was proposed, and the seismic performance was proposed. To study the seismic performance such as failure mode, hysteretic behavior, deformation, ductility of the specimen, and the influence of the outsourcing steel pipe on the mechanical performance of the specimens, the comparative tests of four full-scale specimens under low cyclic reciprocating load under a high axial compression ratio were carried out. The test results show that the monolithic column assembled with outsourced steel has better overall performance, and the failure of the specimen is the large eccentric compression failure with good ductility. The hysteresis and skeleton curves of the assembled columns are similar to the cast-in-site concrete column under the same conditions, which have a good ductility and energy dissipation capacity. It was established that increasing the thickness of the outer steel plate does not significantly improve the mechanical performance of the component when the load-bearing capacity of members satisfies the design requirements. The research results can provide a reference for theoretical research and practical engineering applications of assembled monolithic concrete column connections.