Loop Joint Research Articles

Effect of loop reinforcement joints on the strength of eccentrically compressed reinforced concrete structures

Introduction. Using loop joints of working reinforcement in flexural reinforced concrete members reduces labor costs when installing reinforcement cages at the construction site. However, the analysis of the available research showed that they were carried out mainly for flexural members. In this regard, additional experimental studies were carried out to assess the effect of various types of design solutions of loop reinforcement joints on the strength of normal sections of eccentrically compressed reinforced concrete elements.Aim. To obtain the results of experimental studies and assess the effect of design solutions of loop reinforcement joints on the strength of eccentrically compressed reinforced concrete elements.Materials and methods. The research involved the results of tests of eccentrically compressed reinforced concrete elements with loop joints of working reinforcement. As part of the research, 7 series of samples with different design solutions of loop joints were tested. The total number of samples in the research comprised 22 items.Results. The research revealed the effect of design solutions of loop reinforcement joints on the strength of eccentrically compressed reinforced concrete elements – on average from 3 to 14 %, depending on the design solution of the loop joint.Conclusions. It was found that the design of eccentrically compressed elements should be carried out taking into account the design of the loop joint of longitudinal reinforcement.

Tensile analysis of loop joints with different overlap lengths

ABSTRACT In order to achieve rapid bridge construction, on-site wet joint joining techniques for prefabricated bridge decks are commonly used. The primary method involves mainly lap welding, but this form poses some drawbacks such as difficult lap jointing of two steel bars and a hefty welding workload. To address these issues, this study conducts model experiments on the unwelded structure of loop joints. We compare and analyze the displacement, crack distribution, crack development process, and strain variability of loop joints across three different overlap lengths, along with one type of straight bar lap-welded wet joints. It is observed that, despite the comparable ultimate tensile capacity of loop joints with the main rib to that of the welded wet joint with the main rib, the failure mode varies, and the crack direction changes with the overlap length. From a structural stress perspective, if the U-bar of the loop joint meets a specific overlap length, the wet joint adequately fulfills stress requirements and can be applied in practical engineering.

ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ КОНСТРУКЦИЙ С ПЕТЛЕВЫМИ СТЫКАМИ АРМАТУРЫ

The article describes the statement of a problem of research of the stress-strain state of reinforced concrete monolithic structures with loop joints of rebar using the finite element method. A review of plastic damaged concrete model, a description of its basic parameters and their selection by the example of the problem of verification of mathematical material model by the results of full-scale tests of concrete prism and beam with a loop joint over a static load have been presented. The detailed description of the model parameters, diagrams of concrete and reinforcement state, including stress-strain diagrams with regard to the models features, as well as graphs comparing the experimental and numerical research of a concrete prism and a bendable reinforced concrete beam with a loop joint, including a model of concrete, and reinforcement model are presented. The results of numerical calculations obtained stresses in the reinforcement of 514 MPa, which is close to those resulting from the full-scale experiment of 550 MPa (Fig. 8). The value of deflection when the failure load in the experiment was 16.7 mm, in the FE model it was 18.07 mm.

Development of Narrow Loop Joint for Precast Concrete Slabs with Fiber-Reinforced Mortar: Experimental Investigation of Material Properties and Flexural Behavior of Joint

In the replacement of the reinforced concrete slab in existing steel girder bridges, a loop joint is commonly used to join precast concrete slabs on site. However, a relatively wide joint is needed, and considerable time and effort are consumed to construct the joint due to the addition of transverse reinforcements to the joint on site. These disadvantages affect the progress of on-site construction and should be addressed, especially when this method is applied to highway bridges, where early traffic opening is necessary in many cases. This study proposes a narrow loop joint that has fiber-reinforced mortar without transverse reinforcements. Several material tests were conducted to determine a suitable material for the joint. A series of flexural loading tests of slabs was conducted to investigate the flexural behavior of the proposed loop joint with the selected material (polyvinyl alcohol (PVA) fibers). The results showed that the flexural capacity and deformation performance of the proposed joint with PVA fibers are equivalent to those of the conventional loop joint.

Development of Improved Loop Joint Applied for Precast PC Deck Slab

Development of Improved Loop Joint Applied for Precast PC Deck Slab

Nature of change of logarithmic decrement as a result of cracking in the beams with loop joints

Paying attention to the quite wide spreading of precast and cast-in-situ reinforced concrete in Ukraine, it was necessary to expand the scope of application of various butt joints. In particular, the use of loop rebar joints is itself one of the main design decisions that determines the industrial implementation of construction, primarily hydraulic structures. Loop rebar joints connect elements for assembling precast-monolithic reinforced concrete elements without the use of welding. A large territory of south-western and southern parts of Ukraine is classified as seismically dangerous. The use of modern probabilistic technologies at the design and operation stages of construction projects improves the accuracy of hazardous seismic load estimates and allows to optimize the probable losses from the negative impact of earthquakes. The proper assessment of the level of seismic impact depends on knowledge of the pattern in the logarithmic decrement changes as a result of building structures and buildings damage. Available information does not give a clear understanding of this pattern. A comparative analysis of the change in the logarithmic damping decrement of vibrations because of cracking in beams with a loop joint was carried out. The loop joint was located in the clean bending zone of beam, with keyed and keyless execution of the ends of the joined elements. The data for analysis were obtained from the experiment. We use the power method to achieve the objectives − the instant load removal method. As a result the nature of the change in the logarithmic damping decrement of the beam in case of violation of the integrity of the loop joint zone was established. The values of the logarithmic decrement in the beams with key joints were comparable with the similar values obtained for beams without joints. At the same time, the absolute values of the decrement in beams with keyless loop joints were maximum in these studies .

Numerical study of the behaviour of loop bar splicing in joints of reinforced concrete structures

Abstract Sometimes straight bar splicing takes up too much space in a reinforced concrete structure due to the required overlapping length. Therefore, in limited space situations, loop joints may be a good solution, which has been spread in civil construction, although there are very few studies about it. The aim of the present work is to study the loop joint behavior in reinforced concrete structures under tension. Three dimensional numerical simulations are made using the software DIANA®. Firstly, the calibration of the numerical model based on experimental tests of the literature is performed, followed by parametric analyses varying geometric parameters of the concrete elements and reinforcement. The results indicate that arranging the bars as close as possible to a maximum spacing of 60 mm between axes and considering a minimum splice length equal to the bend diameter of the loops may be an ideal situation for the behavior of this type of connection.

New structural joint by rebar looping applied to staged box girder bridge construction. Static tests

AbstractThe paper describes the design, development and experimental checking of a modified type of structural joint with limited length between concrete segments cast in‐situ. The design concept is based on the developed length of an anchorage hook stiffened by transverse reinforcement bars and is particularly suited for the case of in‐situ construction of staged box girder bridges, with the intention of possibly using lighter scaffolding.The studies concentrated on the strength, stiffness and serviceability of the proposed joint are presented. The research work comprises the bending behaviour of reinforced concrete slabs with loop joints with regard to the diameter of the loop bar, loop joint width and ultimate and fatigue load. The results are compared to the behaviour of reinforced concrete slabs without joints. A total of 16 slabs were tested with static and fatigue loading tests. The present paper evaluates the flexural behaviour in static loading tests. The results of fatigue tests have also shown excellent performance.In the static tests, crack widths and cracking pattern were observed at service load levels, and the ultimate behaviour was evaluated by means of tests to failure.From the test results, the service performance of the loop joints was confirmed to be similar to slabs without joints. The static loading tests confirm the good performance and effectiveness of this loop joint type under static loading. Details of the loop joint design criteria are also proposed.

소켓연결 방식을 이용한 프리스트레스트 콘크리트 제형 거더의 구조성능 평가

In this study, in order to asses the structural performance of trapezoidal PSC girder using a socket joint system and it is possible to calculate the optimized cross-section of the web element tests were carried out for each specimens. we conducted a socket joint performance test, web bending and shear performance tests and all tests were performed at 4 point loading method. The initial crack load of socket joint specimen was significantly lower than the reference specimen but post peak behavior was no significant differences. And the length of the loop joint of the reinforcing bars had no significant effect on the maximum load. As a web shear tests, to obtain a maximum load of the specimen has a prestressing rod reinforced at tension side. As a web flexural tests, to obtain higher diagonal cracking load in specimen of reinforced using prestressing rod than reference specimen.

Crack Width Control on Concrete Slab using Half-Depth Precast Panels with Loop Joints

반두께 프리캐스트 콘크리트 바닥판의 적용이 증가함에 따라, 프리캐스트 구조물 간의 연결에 대한 연구가 증가하고 있다. 또한, 프리캐스트 패널을 갖는 합성바닥판에서 패널간에는 횡방향 이음부의 연속적인 거동이 요구된다. 이 논문에서는 루프이음 방식을 적용하여 교축방향 패널과 패널사이의 이음부에 구조적 연속성과 성능을 평가하였다. 실험결과로부터 바닥판의 연속성 확보를 위한 루프철근 이음부의 휨강도 및 균열제어의 연속성을 확인하였다. 실험결과 루프이음 철근 간격을 좁게 한 경우의 휨강도가 1.52배 증진되는 효과를 보였다. 또한, 루프이음부에 횡방향 철근은 균열제어에 매우 효율적임을 확인하였다. As the half-depth precast concrete decks are increasingly applied to the construction sites, researches on connection details have been increased. For design of concrete bridge deck with half-depth precast panels, it is required to provide appropriate details of transverse loop joints between panels. In this paper, the structural performance of precast decks was evaluated to investigate continuity of the proposed loop joint details. From the results, the validity of the joints for the continuity of deck was observed in the aspect of flexural strength and crack control. The ultimate strength increased 1.52 times as the reinforcement spacing in the joint was reduced. In terms of crack control, direct crack width calculation for the loop joint showed appropriate results comparing with measured crack width.

Structural Performance of Precast Concrete Arch with Reinforced Joint

내구성과 미관성이 우수한 석조 아치교량은 단경간 교량으로서 가장 오래되고 경험적으로 시공되었던 구조물로서 유럽에서는 지금까지도 현장에 시공되고 있으며, 이에 대한 활발한 연구가 진행되고 있다. 그러나 국내에서는 시공법의 비효율성과 비경제성으로 인해 교량 목적으로 시공되는 경우는 거의 없는 상태이다. 따라서 본 연구에서는 기존 연구자들이 제안한 시스템에서 구조성능의 향상이 가능한 보강된 이음부의 접합방법을 제안하였다. 제안된 이음부는 횡방향 루프이음과 종방향 보강근을 적용한 형식으로 프리캐스트 콘크리트 블록으로 이루어진 아치에 적용하여 실험을 통해서 구조적 성능을 평가하였다. 실험결과, 보강된 이음부는 소량의 보강근으로도 블록 상호 간의 상대변위와 힌지거동을 억제시켜 기존의 형식보다 충분한 내력을 향상시킬 수 있을 것으로 판단된다. The masonry stone arch bridge, due to its superior durability and aesthetics, has been one of the oldest and popular types of short span bridges. In Europe, this type of bridges have been continuously constructed, and numerous related researches have been conducted until recently. However, there are few construction cases in Korea since the economic efficiency and the construction effectiveness is not contentable. Therefore, this study proposed the reinforced joint to improve structural performance of the conventional arch systems which is proposed by previous researchers. The structural performance of the proposed reinforced joint, which consists of the transverse loop joint and the longitudinal reinforcement, is validated by experimental test of an arch bridge which is constructed using precast concrete segments. Based on this results of the experimental test, it is concluded that the strength of arch bridges can be enhanced by applying the proposed reinforced joints since the reinforced joint restrains hinge behavior and relative displacement between segments with a little reinforcement.

Approximate inverse Ising models close to a Bethe reference point

We investigate different ways of generating approximate solutions to the inverse Ising problem (IIP). Our approach consists in taking as a starting point for further perturbation procedures, a Bethe mean-field solution obtained with a maximum spanning tree (MST) of pairwise mutual information, which we refer to as the Bethe reference point. We consider three different ways of following this idea: in the first one, we discuss a greedy procedure by which optimal links to be added starting from the Bethe reference point are selected and calibrated iteratively; the second one is based on the observation that the natural gradient can be computed analytically at the Bethe point; the last one deals with loop corrections to the Bethe point. Assuming no external field and using a dual transform we develop a dual loop joint model based on a well-chosen cycle basis. This leads us to identify a subclass of planar models, which we refer to as dual-loop-free models, having possibly many loops, but characterized by a singly connected dual factor graph, for which the partition function and the linear response can be computed exactly in respectively O(N) and O(N2) operations, thanks to a dual weight propagation (DWP) message passing procedure that we set up. When restricted to this subclass of models, the inverse Ising problem being convex, becomes tractable at any temperature. Numerical experiments show that this can serve to some extent as a good approximation for models with dual loops.

New Structural Joint by Rebar Looping Applied to Segmental Bridge Construction: Fatigue Strength Tests

The objective of this research has been to design, develop, and evaluate experimentally a modified type of construction joint of limited length between concrete slab segments. The design concept is based on an anchorage hook of reduced development length stiffened by transverse reinforcement bars. The purpose of this paper is to investigate the mechanical behavior of the joint in terms of stiffness and strength for an application that requires high durability, which often leads to serviceability problems such as cracking and water leakage at transverse joints. This can regularly appear in bridges. Additionally, bridge decks are structures that are subjected to repeated loading such as traffic loads, making it necessary to evaluate the behavior of joints under fatigue load. Therefore, studies focusing on the strength, stiffness, and serviceability of the joints must be carried out. This paper investigates experimentally the fatigue behavior and strength of loop joints with regard to the loop bar diameter, loop joint width, and applied load ranges. These results were compared with the behavior of RC slabs without joints. A total of eight slabs were fabricated for fatigue loading tests, and the failures of the different specimens (with loop joints and without) were obtained. From the test results, the mechanical behavior of the slabs with loop joints was confirmed to be similar to that of the slabs without joints. The experimental loop joint design was found to perform correctly under fatigue loads.

604 コンベヤベルトの損傷検知機能を有するゴムSteel組紐複合体のループ継手部の疲労特性の改善(GS-3 衝撃,疲労,疲労設計)

604 コンベヤベルトの損傷検知機能を有するゴムSteel組紐複合体のループ継手部の疲労特性の改善(GS-3 衝撃,疲労,疲労設計)

Using the Single Reciprocal Screw to Confirm Mobility of a Six-Revolute Linkage

Overconstrained kinematic chains have been discovered mostly by analytical or geometrical means or through a synthesizing procedure. In a few instances they have succumbed to computer-aided methods, and those solutions can, in effect, be reduced to a single one. This loop, of six revolutes, is described by parametric conditions that provide little information about its physical make-up. The existence of a lone screw reciprocal to the system defined by the loop's joint screws is the basis here for demonstrating analytically the linkage's mobility and determining its mode of assembly. In addition, it is shown that seven new linkages can be developed from this solution as isomeric variants.

Experimental study on static and fatigue strength of loop joints

In order to investigate the stiffness and strength of the loop joints, experimental studies were conducted. Two types of loading tests were performed which are static loading tests and fatigue loading tests. The test variables are the diameter of the loop bars and the width of the loop joint. Cracking, ultimate behaviour, ductility and fatigue behaviour of the loop joints were observed and compared with the behavior of RC beams without joints. From the test results, the mechanical behaviour of the loop joints was confirmed similar to that of ordinary RC beams without joints if the joint widths were enough in terms of development length concept for the anchorage of hook reinforcement. It was investigated that the overlapping section within the loop joint has similar or rather good mechanical characteristics to the RC beam section without joints. However, it is necessary to notice that a reduction of stiffness and strength could be occurring at the casting interface region in the loop joint RC members, especially with inadequate narrow joint widths. The design concept of the development length for the anchorage of hook reinforcement for the design of details of loop joints is recommended. Consequently, details of the loop joints were suggested and based on the fatigue test results, a S–N curve for the loop joints was proposed.

On Certain Surfaces and Curves Associated with the Bennett Linkage

Although the subject of many more investigations than any other skew linkage, the Bennett loop does not yield up its properties easily. Recent work has revealed the axodes, which putatively determine its higher-order kinematics, and some of the derivable geometric features, but the study remains incomplete. The present paper uncovers previously hidden characteristics of significance, namely, the operative regulus in the fixed axode's central tangent surface and the consequent parametric equation of its curve of striction. The approach is extended to an examination of the hyperboloid which contains the loop's joint axes.