Maria Anna Polak

Retrofit of Slab Column Interior Connections Using Shear Bolts

Shear bolts are a new type of reinforcement developed for punching shear strengthening and retrofit of existing slab-column connections. The shear bolt consists of a headed vertical rod threaded at the other end for anchoring using a washer and nut system. The bolts are installed in holes drilled in a slab in concentric perimeters around the column. Previous testing carried out at the University of Waterloo established the feasibility of using shear bolt reinforcement to increase the punching-shear strength and ductility of edge slab column connections. This paper describes an experimental research program in which large-scale models representing interior slab-column connections were tested. Six specimens, 1800 x 1800 x 120 mm, with square columns 150 x 150 mm, were built. Two specimens had openings constructed near the column. These two, and an additional three, specimens were reinforced using the shear bolt system. One slab was without the shear bolts and served as a control specimen. The test results are presented in terms of deflections, strains, and crack width. It was found that the use of shear bolts increased the strength of the connection and significantly improved the ductility.

MODELING PUNCHING SHEAR OF REINFORCED CONCRETE SLABS USING LAYERED FINITE ELEMENTS

The paper examines the applicability of the finite element, layered, shell formulation in the global analysis of reinforced concrete slabs when subjected to high, concentrated transverse loads. The formulation incorporates quadratic, degenerate, isoparametric shell elements. A significant feature of these elements is their ability to take into account out-of-plane shear response. This allows the implementation of a three-dimensional constitutive model for the evaluation of the stiffness matrix. The proposed formulation allows the use of out-of-plane reinforcement in the elements. Through the consideration of the three-dimensional states of strain and stress in each layer, the model can predict the failure of structures caused by either flexure or punching shear. The paper presents and discusses the essential features of the proposed formulation that are related to the transverse shear model. The formulation has been checked against experimental results of tests on slabs subjected to punching shear. A parametric study has also been undertaken to determine the influence of several parameters on the behavior of slabs with and without stirrups.

Rayleigh wave propagation for the detection of near surface discontinuities: Finite element modeling

The paper presents a finite element study designed to gain physical insight into the effect of surface discontinuities on Rayleigh wave propagation in structural elements. In particular, a series of array measurements at various locations within a plate are simulated and compared with experimental measurements. Conversion of array measurements into the frequency-wavenumber domain reveals propagating Lamb modes, which are used to define Rayleigh wave motion. Numerical results show that Rayleigh waves measured after passing a fracture are composed of long wavelength Rayleigh wave energy propagating past the slot and short wavelength Rayleigh wave energy formed behind the slot.

COMPUTER VISION TECHNIQUES FOR AUTOMATIC STRUCTURAL ASSESSMENT OF UNDERGROUND PIPES

Pipeline surface defects such as cracks cause major problems for asset managers, particularly when the pipe is buried under the ground. The manual inspection of surface defects in the underground pipes has a number of drawbacks, including subjectivity, varying standards, and high costs. An automatic inspection system using image processing and artificial intelligence techniques can overcome many of these disadvantages and offer asset managers an opportunity to significantly improve quality and reduce costs. This article presents a system for the application of computer vision techniques to the automatic assessment of the structural condition of underground pipes. The algorithm consists of image preprocessing, a sequence of morphological operations to accurately extract pipe joints and laterals (where smaller pipe is connected to main bigger pipe), and statistical filters for detection of surface cracks in the pipeline network. The proposed approach can be completely automated and has been tested on over 1,000 scanned images of underground pipes from major cities in North America.

Mechanical modelling for pipes in horizontal directional drilling

This paper presents a new technique to predict forces and deformations of pipes installed underground by horizontal directional drilling (HDD). The proposed technique consists of several models each describing different aspects of mechanics of HDD. It allows prediction of the shape of the pipe in the borepath. Based on the pipe shape, shape of the borepath and pipe stiffness, the contact forces between the pipe and the borepath are calculated. The contact forces cause friction and thus axial pulling force is induced to equilibrate the frictional forces and the weight of the pipe. The analytical model is used to study the stresses and strains on two pipes that were tested in the field. The theoretical results are compared with the strains measured in the field.

Detection of Surface Breaking Cracks in Concrete Members Using Rayleigh Waves

This study examines the use of Rayleigh waves for the detection and sizing of surface-breaking cracks in concrete members. First, finite element simulations are performed to define the conditions for Rayleigh wave propagation in members with rectangular cross-section followed by an experimental study with a concrete beam. Time histories recorded at different locations are 2D Fourier transformed into the frequency-wavenumber domain to enhance interpretation and data analysis. Rayleigh waves form at depths less than half the beam depth. With the introduction of a slot, Rayleigh waves are not observed behind the slot, except for the shortest slot depth, and the slot depth cannot be estimated in the frequency-wavenumber domain. Autospectrum calculations reveal strong Rayleigh wave reflections in front of the slot and by can be used to estimate slot depth when the wavelength is less than half the beam depth.

NEW SHEAR STRENGTHENING TECHNIQUE FOR CONCRETE SLAB-COLUMN CONNECTIONS

This paper presents an experimental program that involved tests on full-scale RC slab-column edge connections. The aim of this work was to examine a new method for strengthening existing RC slabs for punching shear. The new strengthening technique consists of shear bolts externally installed in holes drilled through the slab thickness. Different configurations of the shear bolts around the column were tested. Four slabs were strengthened and 2 slabs, used as control specimens, did not contain any shear reinforcement. Two of the tested slabs (1 strengthened and 1 control) contained openings in the area of the column. Slab dimensions were 1540 x 1020 x 120 mm with square columns. The openings, where present, were square and directly adjacent to the inner face of the column. The slabs were tested to failure under monotonic vertical shear forces and unbalanced moments. The presence of shear bolts substantially increased the punching capacity and ductility of the connections.

A Tensile Strain Hardening Test Indicator of Environmental Stress Cracking Resistance

Environmental stress cracking resistance (ESCR) is an important indicator of performance for high density polyethylene (HDPE) in structural and polymer pipe applications. The commonly used test for determining ESCR of HDPE can be time consuming and rather imprecise. A tensile strain hardening test was recently proposed to offer a faster way to characterize ESCR of polyethylene. In this paper, a practical approach is adopted whereby the test is extended to room temperature and shown to relate reliably to the ESCR of HDPE. Several HDPE resins (including pipe‐grade resins) are analyzed at strain rates of 0.5 mm/min and 7 mm/min to compare the effect of strain rate. Comparisons between the conventional ESCR test method and the strain hardening test show that strain hardening can be used to rank ESCR of HDPE in a reliable fashion. In our study the more direct measure of “hardening stiffness” is used to compare resins instead of strain hardening modulus. Because no true stress‐strain measurement is needed, this is a much simpler test method than other methods previously suggested. In addition, the use of the natural drawing ratio (NDR) as ESCR ranking indicator is examined. Results show that NDR can also be employed as a strain rate‐independent indicator of ESCR of HDPE. The test proposed herein is practical, simple and precise, and hence a more reliable indicator of ESCR performance of HDPE.

Reinforced Concrete Slab-Column Edge Connections with Openings

The paper reports the results of 14 tests, which address the influence of openings on the behaviour of reinforced concrete flat slab-column edge connections. The slabs were subjected to vertical loads and moments with constant moment-to-shear ratios. The test parameters were: the location of openings around the column, the size of openings, the moment-to-shear ratio, and the existence of shear reinforcement. The test specimens were large scale and represented a portion of a slab bounded by the lines of contraflexure around the column.

Wave propagation in thin Plexiglas plates: implications for Rayleigh waves

Abstract Two-dimensional (2D) experimental models are often used to study wave propagation problems. The advantages of using 2D experimental models, as opposed to 3D models, is the reduction of both extraneous reflections and mathematical complexity. Further, many structural elements conform to this geometry. The following study examines Rayleigh wave motion in thin Plexiglas sheets. Source–receiver time domain measurements were made at different locations on the Plexiglas sheet. The time–distance space was 2D-Fourier transformed into the frequency–wavenumber space to facilitate the analysis of wave modes propagating in the Plexiglas sheet. Experimental results showed that fundamental symmetric (S 0 ) and antisymmetric (A 0 ) Lamb waves propagated through the plate. Along the thickness of the plate, a non-dispersive Rayleigh wave was generated. Lamb waves were found to interfere with the Rayleigh wave. The assumption of generalized plane stress is preserved if higher mode Lamb waves have low energy content.