STR-908: EFFECT OF GEOMETRIC IMPERFECTIONS ON THE CAPACITY OF CONICAL STEEL TANKS UNDER HYDRODYNAMIC PRESSURE

Liquid tanks in the form of truncated steel cones are commonly used for liquid storage in North America and in other locations. The main cause of failure, for conical steel tanks in particular, which was identified in most of the failure cases, is the buckling of the tank’s shell at locations of maximum compressive stress. Being constructed of steel, geometric imperfections in the conical tank walls will exist and their amplitude will be dependent on the quality controls applied by the builder. Such geometric imperfections play an important role in defining the buckling capacity of shell structures in general. Some studies found in the literature assessed the effect of geometric imperfections on the buckling capacity of steel tanks. However, most of these studies focused on hydrostatic pressure and not on hydrodynamic pressure that is induced on the tank walls when the tank base is subjected to either horizontal or vertical ground excitations. In this study, an expression for the critical imperfection wave length is obtained and the effect of the geometric imperfections’ amplitude on the buckling capacity of conical steel tanks is assessed numerically under hydrodynamic pressure due to horizontal and vertical ground excitations. The study is conducted numerically through non-linear static pushover analysis using an in-house finite element model that accounts for the geometric and material nonlinear effects

STR-994: INVESTIGATION OF L-SHAPED LOW-RISE AND HIGH-RISE BUILDINGS RESPONSE TO NBCC 2005 AND 2010 SEISMIC LOADS

The current study builds on a previous study conducted by the authors that investigated the seismic provisions of the National Building Code of Canada (NBCC) 2005 and 2010, pertaining to the loading and analysis of irregular L-shaped buildings. The study uses low-rise and high-rise L-shaped buildings as case studies. Three-dimensional finite element models of the two irregular L-shaped buildings were developed and discussed in the previous study. The lateral resisting system of the low-rise buildings consists of concrete shear walls, while the high-rise building consists of a combination of concrete shear walls and concrete rigid frames. Low and high-rise concrete buildings are modelled with the assumption of fully rigid floor diaphragms for computational efficiency. In the current the study, the effect of using rigid and semi-rigid diaphragms to simulate structural floors on the structure response to lateral loads is investigated. Significant change in the dynamic response and lateral force distribution along both buildings’ height due to the use of semi-rigid diaphragms is noticed. In addition, a negligible contribution due to the effective inertia, due to cracking of concrete shear walls on the overall dynamic response of both buildings is observed. The study shows that the variation of post-cracking stiffness for concrete slabs significantly affect the stiffness and the natural frequency of the buildings

NDM-524: CASE STUDY TO ASSESS THE SENSITIVITY OF PRESTRESSED CONCRETE POLES TO TORNADOES

Transmission line structures play a vital role in transmitting electricity from the source of production to the distribution system. The main components of a transmission line are the conductors, the insulator strings, the ground wires and the supporting towers. Among the different types of supporting towers, prestressed concrete transmission poles have the advantages of low installation and maintenance costs, appropriate delivery time, and corrosion resistivity. To the best of the authors’ knowledge, this paper represents the first investigation conducted to assess the response of cantilever prestressed concrete poles to tornadoes. The localized nature of the tornadoes and the extended length of the conductors introduce some challenges in predicting the critical response of power transmission towers to tornadoes. The current study is conducted numerically using an in-house numerical model that includes the following: (1) a three-dimensional tornado wind field developed using computational fluid dynamics simulations; (2) a non-linear simulation of the structural behaviour of a prestressed concrete transmission poles taking into account the non-linear behaviour of the concrete and of the prestressed strands, and (3) a simulation of the non-linear behaviour of the conductors including the effects of the pretension force, sagging, the insulator’s stiffness and the non-uniform distribution of wind loads. Details of this numerical model are briefly discussed in this paper. A case study is considered to assess the importance of including the effect of tornadoes in the design of prestressed concrete poles

NDM-536: EFFECT OF WIND SPEED AND TERRAIN EXPOSURE ON THE WIND PRESSURES FOR ELEVATED STEEL CONICAL TANKS

Steel liquid storage tanks in the form of truncated cones are commonly used as containment vessels for water supply or storing chemicals. A number of failures have been recorded in the past few decades for steel liquid tanks and silos under wind loading. A steel conical tank vessel will have a relatively small thickness making it susceptible to buckling under wind loads especially when they are not fully-filled. In this study, a wind tunnel pressure test is performed on an elevated conical tank in order to estimate the external wind pressures when immersed into a boundary layer. The tested tank configuration represents combined conical tanks where the cone is capped with a cylinder. In addition, the effect of terrain exposure and wind speed on the pressure values and wind forces is assessed. The mean and rms pressure coefficients are presented for different test cases in addition to the mean and rms total drag forces that are obtained by integrating the pressure coefficient over the tank model’s surface. It is found that the total mean and rms drag forces are highly-dependent on Reynolds number which is a function of wind speed and they have a maximum value at mid-height for the lower cylinder, at top for the conical part, and at bottom for the upper cylindrical part

NDM-530: AERODYNAMIC OPTIMIZATION TO REDUCE WIND LOADS ON TALL BUILDINGS

Wind is one of the governing load cases for tall building design, which produces high level of straining actions, deflections and lateral and transverse vibrations. Keeping those vibrations within the comfort limits is becoming a key aspect in tall building design, especially for buildings with high aspect ratio. Improving the aerodynamic performance of the tall building by modifying its shape can lower building motions, which reduces the additional expenses for external damping systems and alleviate the high cost associated with lateral support systems. In the present study, an aerodynamic shape optimization procedure is developed by combining Computational Fluid Dynamics (CFD), optimization algorithm and Artificial Neural Network (ANN). The developed procedure utilizes ANN as a surrogate model for evaluating aerodynamic properties, which is pre-trained using two-dimensional CFD analysis. The current study investigates the validity of the developed procedure by conducting a high accuracy, three-dimensional Large Eddy Simulation (LES) based analysis on the optimal building shapes. It was observed that utilizing two-dimensional CFD simulations in the optimization procedure can help identify effective cross-sections of tall buildings

STR-860: COST ANALYSIS OF CONICAL TANKS; COMPARISON BETWEEN REINFORCED CONCRETE AND STEEL

This paper provides a cost analysis case study to compare the effectiveness of using reinforced concrete versus steel as a construction material for conical tanks. Simplified design approaches, which were developed in previous investigations, are utilized to design a wide range of reinforced concrete conical tanks and steel counterparts having three different capacities (500 m3, 1750 m3 and 3000 m3). The cost analysis is conducted for each of the concrete and steel tanks. This analysis includes the cost of material, formwork, labour and life-cycle cost. Also, a general study of the effect of tank dimensions on the cost is provided. The results of this study show that steel conical tanks are considered as a more economical choice for medium and small capacity tanks, regardless their dimensions. On the other hand, for large capacity conical tanks (3000 m3), the tank dimensions govern which construction material (reinforced concrete or steel) is more cost effective

NDM-534: SENSITIVITY OF WIND INDUCED DYNAMIC RESPONSE OF A TRANSMISSION LINE TO VARIATIONS IN WIND SPEED

This paper studies the dynamic behavior of a multi-span transmission line system under synoptic wind considering various speeds to determine the range of wind speeds in which the system experiences resonance. A finite element numerical model was developed for the purpose of this study. This model is employed to assess the dynamic behavior of a self-supported lattice tower line under various wind speeds. Dynamic Amplification Factor (DAF), defined as the ratio between the peak total response to the peak quasi-static response, is evaluated. It is found that conductors’ responses exhibit large DAF compared to the towers especially at low wind speeds (v ≤ 25 m/s). This results from the low natural frequency of the conductors (0.19 Hz) which is close to the wind load frequency while the natural frequency of the tower is equal to 2.36 Hz. In addition, the conductors’ aerodynamic damping decreases with the decrease of wind speed which leads to higher dynamic effect while the tower’s aerodynamic damping plays a minor role. The results of the dynamic analysis conducted in this study are also used to compare the gust response factors (GFT), defined as the ratio between peak total response to the mean response, to those obtained from the ASCE code (GFT-ASCE). It has been noticed that the gust response factors obtained from the ASCE code lead to conservative peak responses for both towers and conductors of the chosen line

NDM-529: NUMERICAL EVALUATION OF WIND LOADS ON A TALL BUILDING LOCATED IN A CITY CENTRE

Estimation of wind-induced loads and responses is an essential step in tall building design process. Wind load for super tall buildings is commonly evaluated using boundary layer wind tunnel (BLWT) tests. However, the recent development in computational power and techniques is encouraging designers to explore numerical wind load evaluations using a Computational Fluid Dynamics (CFD) approaches. CFD can provide a faster estimation for building loads and responses with lower cost and satisfactory accuracy for preliminary design stages. The current study investigates the accuracy of evaluating wind pressure and building responses of a typical tall building (CAARC building). Two configurations are investigated, which are (1) standalone building and (2) located in a city center. Large Eddy Simulation (LES) numerical model is utilized adopting a newly developed synthesizing turbulence generator named Consistent Discrete Random Flow Generator (CDRFG). The adopted inflow technique is believed to provide good representation of wind statistics (i.e. velocity and turbulence profiles, spectra and coherency). Pressure distributions and building responses from the current study match with those obtained from boundary layer wind tunnel tests. The average difference between the pressure values between the current model and the BLWT is 4%. While the difference in building responses resulted from the LES model to those from BLWT is 6%. It was found that utilizing CDRFG in LES models provides an accurate estimation for building aerodynamic performance in an efficient computational time owing to its capability of supporting parallel processing

NDM-538: WIND TUNNEL TESTING OF A MULTIPLE SPAN AEROELASTIC TRANSMISSION LINE SUBJECTED TO DOWNBURST WIN

A 1:50 scale aeroelastic wind tunnel test for a multi-span transmission line system is conducted at the WindEEE dome under downburst wind. WindEEE is a novel three-dimensional wind testing facility capable of simulating downbursts and tornadoes. This test simulates a transmission line consisting of v-shaped guyed towers holding three conductor bundles. Details about the model design, the wind field and the test setup are provided. A downburst loading case that is critical for the line design and causes unbalanced tension load on the conductors is investigated in the current study. Resulting line responses obtained from the test are compared with a previously developed finite element model by the research group at the University of Western Ontario. The comparison shows a good agreement which validates the finite element models. Results obtained from this test will be very useful to understand the behavior of the lines under downburst wind

NDM-535: STRUCTURAL MODELLING AND VERIFICATION METHODS TO DEVELOP A CABLE ROOF HARNESS RETROFIT SYSTEM

Load paths in light-frame wood structures have historically been nailed connections between the sheathing and rafters, and toenail connections between the rafters and stud walls. However, these connections have poor resistance to uplifting forces, as occurs in high wind speed events, causing sheathing or roof-to-wall-connection (RTWC) failures. The improvements made to building codes after Hurricane Andrew affected only new construction, and the economic losses caused by roof failures in homes built prior to 1993 from Hurricane Katrina pointed to a need to retrofit older structures. This paper will investigate the design, analysis, and testing of a temporary cable-netting roof harness as an alternative to relatively expensive and invasive retrofitting options. To do this, a non-linear finite element analysis (FEA) is performed to model a typical light-frame wood structure with the roof harness, which is then validated through test results. After, as a comparative study, scaled down versions of the structure with and without the roof harness are created and tested using real wind load until failure at the WindEEE facility. This is done to assess the efficacy of the retrofit system. Corresponding FEA and computational fluid dynamics (CFD) models are then created to simulate the test