Development and challenges in finite element modelling of post-installed anchors in concrete

Finite element analysis (FEA) has been used as a successful supplement to experimental testing in various studies for simulation of anchorage behaviour. Throughout the years, researchers have employed different modelling techniques in various FEA packages to capture the behaviour of post-installed anchors. However, the vast amount of knowledge accrued is yet to be reviewed. This article critically reviews all aspects of FEA from pre-processing to post-processing and provides a comprehensive review of published literature on FEA studies for predicting the behaviour of post-installed anchorage systems. Most current efforts focus on investigating failure mechanism of anchors in uncracked concrete under tensile loading. Findings show that developing finite element model for post-installed anchorage in concrete is very challenging due to complex geometrical configuration of anchors, difficulty in modelling concrete–anchor interface and lack of reliable information on selecting material properties and parameters. The analysis identified key gaps in research related to the effect of geometrical simplification, anchor subjected to dynamic loading and anchor performance in cracked concrete which needs attention in future research. This review article is a valuable resource in facilitating future research on assessing the performance of post-installed anchorage in concrete with FEA.</p

Experimental and numerical investigation of screw anchors in large crack width

In predicting the capacity of screw anchors under static tensile loading, the Concrete Capacity (CC) method is the state-of-the-art prediction model which covers concrete cone capacities in uncracked and cracked concrete up to 0.3 mm crack width. However, in seismic applications, anchors may be subjected to large crack widths of up to 0.8 mm. With large crack width, the behaviour of small-sized (typically 6 mm) screw anchors has not been studied. In this study, experimental investigations were conducted for a total of 29 anchors in uncracked and cracked concrete with large crack widths up to 0.8 mm. The experimental results showed that the load-carrying capacity of screw anchors significantly dropped resulting in a reduction factor of 0.13–0.47 for cracked concrete with 0.8 mm crack width (significantly lower than 0.7 assumed by the CC method for a crack width of up to 0.3 mm). This paper focused on developing modelling technique for predicting the performance of screw anchors in cracked concrete with a crack width of up to 0.8 mm since screw anchor in cracked concrete has not been studied using finite element analysis. Three-dimensional finite element models were developed for screw anchors in uncracked and cracked concrete and validated by the experimental results. Further, parametric analysis showed that dilation angle and shape factor are the two most influencing parameters among other of the concrete damage plasticity model.</p

Development and challenges in finite element modelling of post-installed anchors in concrete

Finite element analysis (FEA) has been used as a successful supplement to experimental testing in various studies for simulation of anchorage behaviour. Throughout the years, researchers have employed different modelling techniques in various FEA packages to capture the behaviour of post-installed anchors. However, the vast amount of knowledge accrued is yet to be reviewed. This article critically reviews all aspects of FEA from pre-processing to post-processing and provides a comprehensive review of published literature on FEA studies for predicting the behaviour of post-installed anchorage systems. Most current efforts focus on investigating failure mechanism of anchors in uncracked concrete under tensile loading. Findings show that developing finite element model for post-installed anchorage in concrete is very challenging due to complex geometrical configuration of anchors, difficulty in modelling concrete–anchor interface and lack of reliable information on selecting material properties and parameters. The analysis identified key gaps in research related to the effect of geometrical simplification, anchor subjected to dynamic loading and anchor performance in cracked concrete which needs attention in future research. This review article is a valuable resource in facilitating future research on assessing the performance of post-installed anchorage in concrete with FEA.</p

Development and evaluation of building frames with blind-bolted connections

© 2016 Dr. Tilak PokharelIn general architects and building owners prefer buildings with long span floors which provide open column-free spaces. This is one reason why moment resisting frames using Concrete Filled Steel Tubes (CFST) as the columns have been popular in Japan, China and the USA for many years. In addition, the inherent ductility, efficiency and aesthetic appeal of the concrete filled steel tubes makes them attractive for use as columns. Extensive welding is typically used in the beam-column connections in these frames, but in Australia and other countries field welding is not favoured due to cost and necessity to have specific quality control measures. Shop welding and field bolting is the common practice in those countries. Pre-fabricated diaphragms are used around the column in the joint region in some countries, but they are very expensive. Given that it is difficult to use standard bolts when connecting to the CFSTs, due to the lack of access inside the tube, it is clearly advantageous to develop innovative structural systems that use blind bolted connections. These connections should not require welding on site and the overall system needs to be able to compete with other commonly used structural systems in an economic sense. One perceived advantage of the moment resisting frames is that they will be designed to provide both the lateral and vertical load-resisting system. Hence there would be no need for a structural reinforced concrete core (either pre-cast or in-situ) which is the most commonly used lateral load-resisting system currently in Australia and many other countries. The aim of this research was to develop structural systems for low to mid-rise buildings using moment resisting frames with blind bolted connections with sufficient strength and stiffness to create a lateral force resisting system suitable for low to moderate seismic regions. This aim was achieved by conducting a series of designs, tests and analyses as outlined below. A double T-stub connection is proposed in this study. In the connection, the web of the bottom T-stub acts as a fuse and will limit the load transferred to the blind bolts in tension. This restricts damage to the anchorage of the anchored blind bolts to ensure that they will not pull out or break. The fuse in the connection makes the system a low damage one for very rare earthquakes (2500 year return period earthquake). However, the connection remains strong and stiff under the design level earthquake (500 year return period earthquake) so that drifts are not excessive reducing the risk of damage to the non-structural elements. Designs were carried out for buildings of various heights using moment resisting frames designed as both the lateral and vertical force-resisting systems. These designs employ CFSTs as the columns and have beams consisting of universal beam sections which are composite with a concrete slab (typically a composite slab with a metal deck as well as steel reinforcing bars). In order to design the double T-stub beam-column connections some assumptions were made about the stiffness, strength and ductility that could be achieved. The experimental work and numerical modelling carried out within the thesis has investigated the validity of these assumptions. Tensile tests were carried out on specially modified blind bolts anchored in CFSTs with width (or diameter) to thickness ratios within the expected practical range in order to study the behaviour of these connections under different loading conditions (monotonic and cyclic loading). Detailed finite element analyses were calibrated by comparison with the experimental results and then used to conduct more comprehensive parametric studies to investigate the sensitivity of the tensile behaviour of the anchored blind bolts to variations in these parameters. A sub assemblage test had previously been conducted by Agheshlui (2014). This test was used to calibrate a FE model and then parametric studies were conducted using this model to study the sensitivity of the behaviour of the blind bolted connections to variations in these parameters when being used in low to mid rise buildings. The parameters considered in this study were: the presence of infilled concrete, the use a through bolt, the presence of a composite slab, the wall thickness of the SHS, the compressive strength of the concrete (both infilled concrete and slab concrete), the reinforcement ratio in the slab, bolt sizes and configurations, the T-stub thickness (both flange and web) and the type of blind bolts. Using a case study, the ability of this type of moment resisting frame to withstand a very rare earthquake was checked for different site conditions. A displacement based assessment procedure was used for that purpose. A new practical design philosophy and method were proposed for the design of blind bolted connections in moment resisting frames; it would enable a higher degree of ductility to be achieved in a very rare earthquake event

Create a 3 minute project pitch to showcase your Do-It-Yourself bridge project

The Do-It-Yourself bridge project introduces hands-on experiential learning in the context of design, eningeering and communication of findings. Through this project, students are required to create a 3-minute video and accompanying webpage to showcase and communicate their building process, key findings and reflections from their DIY bridge project. Adobe Premiere Rush and Adobe Express are used to create the digital artefacts

Evaluation of Concrete Material Properties at Early Age

This article investigates the development of the following material properties of concrete with time: compressive strength, tensile strength, modulus of elasticity, and fracture energy. These properties were determined at seven different hydration ages (18 h, 30 h, 48 h, 72 h, 7 days, 14 days, 28 days) for four pure cement concrete mixes totaling 336 specimens tested throughout the study. Experimental data obtained were used to assess the relationship of the above properties with the concrete compressive strength and how these relationships are affected with age. Further, this study investigates prediction models available in literature and recommendations are made for models that are found suitable for application to early age concrete. Results obtained indicate that the relationship between the splitting tensile strength and concrete compressive strength can be approximated with a power function between 0.7 and 0.8, and this correlation is not affected by age. Fracture energy of the concrete and modulus of elasticity values obtained in this study correlate well with the square root of the compressive strength and it was found that this relationship holds true for all hydration ages investigated in this paper. Inverse analysis on the wedge-splitting test was conducted to determine the direct tensile strength. Values of tensile strength obtained from the inverse analysis have been validated numerically by carrying out finite element analysis on the wedge split, and anchor pull-out tests. The ratio of the tensile strength obtained from the inverse analysis to the splitting tensile strength was found to be in the range of 0.5&ndash;0.9 and 0.7 on average

Experimental and analytical behaviour of cogged bars within concrete filled circular tubes

Recent research on steel moment-resisting connection between steel beams and concrete filled steel tubes has shown that there are considerable advantages to be obtained by anchoring the connection to the concrete infill within the tube using anchors in blind bolts. In the research reported here, extensive experimental tests and numerical analyses have been performed to study the anchorage behaviour of cogged deformed reinforcing bars within concrete filled circular steel tubes. This data in essential knowledge for the design of the steel connections that use anchored blind bolts, both for strength and stiffness. A series of pull-out tests were conducted using steel tubes with different diameter to thickness ratios under monotonic and cyclic loading. Both hoop strains and longitudinal strains in the tubes were measured together with applied load and slip. Various lead-in lengths before the bend and length of tailed extension after the bend were examined. These dimensions were limited by the dimensions of the steel tube and did not meet the requirements for "standard" cogs as specified in concrete standards such as AS 3600 and ACI 318. Nevertheless, all of the tested specimens failed by bar fracture outside the steel tubes. A comprehensive 3D Finite Element model was developed to simulate the pull-out tests. The FE model took into account material nonlinearities, deformations in reinforcing bars and interactions between different surfaces. The FE results were found to be in good agreement with experimental results. This model was then used to conduct parametric studies to investigate the influence of the confinement provided by the steel tube on the infilled concrete

Tensile Behavior of Small Screw Anchors under Cyclic Crack Openings

Small-sized anchors (typically 6 mm [0.24 in.]) are commonly used for nonstructural applications. There has been increasing demand for seismic performance of fastenings for nonstructural applications; however, there have been no 6 mm (0.24 in.) size screw anchors with seismic prequalification for large crack width. This study investigated the feasibility of small-sized screw anchors to perform under tension loading in crack widths of up to 0.8 mm (0.03 in.). Tension tests were conducted in cracked concrete with varying crack widths (0.3, 0.5, and 0.8 mm [0.01, 0.02, and 0.03 in.]) under monotonic, pulsating, and varying crack width load protocol. Based on the findings of this study, 6 mm (0.24 in.) screw anchors exhibited load drop and slip behavior in large crack width during the residual capacity test, even for anchors with a deeper embedment. Finite element analysis was conducted to investigate the feasibility of a larger-sized thread width to perform in 0.8 mm (0.03 in.) crack width.</p