EFFECT OF EDGE DISTANCES ON STIFFNESS OF SHEAR-TENSION MODE IN GLULAM CONNECTIONS WITH INCLINED SCREWS

The effects of edge distances on stiffness in glulam connections with inclined self-tapping screws were studied in this paper. Under four anchorage angles (A-45°, A-60°, A-75°, A-90°) and three edge distances (EG-2D, EG-4D, EG-6D) conditions, the shear-tension tests were carried out on the timber structure connections with inclined self-tapping screws, and the stiffness and other properties of the connections were tested. Based on the results, the effects of edge distances on stiffness in joints were quantified using the equivalent energy elastic-plastic (EEEP) model. The results showed that the edge distances had a certain impact on the yield mode and load-carrying performance of the joints. Within a certain range of variation, as the edge distance increased, the stiffness of the connections increased gradually, showing a positive correlation. The stiffness of specimen EG-2D is 4.41 kN·mm-1. The stiffness of specimen EG-4D is 10.04 kN·mm-1, which increasesby 128% compared with the specimen EG-2D. The stiffness of specimen EG-6D is 12.08 kN·mm-1, which increases by 174% compared with the specimen EG-2D. However, the ductility coefficient, yielding load, and energy dissipatinghave no significant change. Within a reasonable edge distance, only ductile damage occurred.

Shear Behavior of Single Cast-in Anchor Simulating Characteristics of Bridge Bearing Anchor

A bridge bearing anchor transmits various loads of a superstructure to a substructure. However, most anchors are generally designed without consideration of characteristics such as concrete pedestal, grout bedding, and anchor socket. Therefore, this study investigated the shear behavior of anchors in accordance with the edge distance, embedment depth, compressive strength of concrete, and height of the concrete pedestal in order to simulate the practical characteristics of the bridge bearing anchors. The actual shear capacity of the anchor differs from the shear strength calculated by the ACI 318 Code; especially, the importance of the embedment depth is underestimated in the code. An increase in the height of the concrete pedestal has a negative effect on the shear capacity because of the stress concentration. The grout is fractured prior to the occurrence of local damages in concrete, resulting in a secondary moment. As a result, the effect of the level arm is observed. An equation, which can predict the relative cracking degree of concrete, is proposed by analyzing the displacement of grout and concrete. High strain occurs in the stirrups close to the anchor, and the behavior of the strain is more influenced by the embedment depth than the edge distance. Finally, the design equation of concrete breakout strength is modified to predict the more precise shear resistance of a bridge bearing anchor.

Numerical and Experimental Investigation on Concrete Splitting Failure of Anchor Channels

Concrete splitting failure due to tension load can occur when fastening systems are located close to an edge or corner of a concrete member, especially in thin members. This failure mode has not been extensively investigated for anchor channels. Given the current trend in the construction industry towards more slender concrete members, this failure mode will become more and more relevant. In addition, significantly different design rules in the United States and Europe indicate the need for harmonization between codes. Therefore, an extensive numerical parametric study was carried out to evaluate the influence of member thickness, edge distance, and anchor spacing on the capacity of anchor channels in uncracked and unreinforced concrete members. One of the main findings was that the characteristic edge distance depends on the member thickness and can be larger than 3hef (hef = embedment depth) for thin members. Based on the numerical and experimental test results, modifications of the design recommendations for the splitting failure mode are proposed. Overall, the authors recommend performing the splitting verification separately from the concrete breakout to design anchor channels in thin members more accurately.

MIMO Antenna Based on Metamaterial Frequency Selective Surface

In this paper, a metamaterial-based novel antenna-mutual-coupling reduction structure is proposed and demonstrated. The structure consists of a three-layer metamaterial frequency selective surface (MFSS) superstrate with split-ring resonators and metal grids. The MFSS means metamaterial frequency selective surface that has the metamaterial performance along the substrate and the frequency selective characteristic on the normal direction of the antenna array simultaneously. A 1×2 MIMO antenna that has a short edge-to-edge distance (0.037λ0) is designed as an illustration to demonstrate the validity of the meta-surface for mutual. When loaded with the proposed MFSS, the mutual coupling between the antenna elements is significantly reduced and the gain of the antenna array is improved by 2.5 dBi.

Proposed Qualification Test Procedure to Identify Prestressed Concrete Ties That May Be Susceptible to End-Splitting Cracks

Prestressed concrete ties could develop end-splitting cracks along tendons due to lateral bursting stresses. The lateral bursting stresses can form due to Hoyer effect (change in diameter of the prestressing tendons due to Poisson’s ratio, the jacking force in the tendons, geometrical features, and indent characteristics of the prestressing tendons. End-splitting cracks can occur immediately after de-tensioning procedure in some cases, but they also can be developed during the first weeks after de-tensioning procedure due to sustained lateral stresses exerted by the prestressing tendons. The ability of concrete to resist these bursting stresses without cracking is primarily the function of the thickness of concrete cover, the type of concrete mixture used and the maximum compressive strength of the concrete. The test purpose was to identify tie designs that may be susceptible to end-splitting cracks. The Qualification test will be great tool to identify tie designs that have ability to form end-splitting cracks. The System Qualification Test involves six pre-tensioned concrete prisms with the same prestressing tendons and concrete mixture that is used in the concrete ties, except that the edge distance for the prisms is reduced by approximately 25 percent. If this reduction in edge distance results in longitudinal splitting cracks along the prestressing tendons, then the system (tie design and material selection) may be susceptible to concrete end-splitting cracks. In this case, changes to the design and/or material selection should be made prior to mass production of ties.