Development and evaluation of building frames with blind-bolted connections
Loading...
Citations
Altmetric:
Altmetric::
Download
Associated Records
Authors
File Licence
Editors
Date
2016
Source Title
Journal Title
Journal ISSN
Volume Title
Publisher
Melbourne Authors
Affiliation
Infrastructure Engineering
Document Type
PhD thesis
Subject Code
Citation
Access Status
Open Access
DOI
Access URL
Open Access URL
Open Access at PMC
Linked Resource URL
NHMRC Grant Code
ARC Grant Code
Description
© 2016 Dr. Tilak Pokharel
Abstract
In 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.
Notes
Terms of Use
Keywords
blind bolt, double headed anchored blind bolt, concrete filled square hollow section, experimental analysis, numerical analysis, abaqus, beam column connection, low to moderate seismic region, low to mid rise building, moment rotation, moment resisting connection, sub-assemblage, anchorage