Mustafa Mahamid

The effect of fire loading on a steel frame and connection

The objective of this paper is to investigate the behavior of steel shear connections subjected to severe fire loading conditions. A time-history transient FE analysis is used to model the fire loading. A detailed 3D FE model of an extended shear tab steel connection used in a beam-column joint is developed. The shear tab plate is welded to the web of the column and it is connected to the web of the beam by tightened bolts. The change in steel material properties such as the modulus of elasticity, yield and ultimate strength, and the coefficient of thermal expansion are considered as functions of increasing temperature resulting from fire loading. Stress-strain curves for steel at elevated temperatures are used in the model. Two cases of boundary conditions are studied: one representing a roller at the far end of the beam, another assumes that the beam is pin supported. The base of the column is maintained as a fixed support, while the upper edge of the column is free to deflect in the vertical direction as shown in Figure 2. Pre-tensioning loads are modeled to represent the tightening of the bolts. A fire curve based on tests conducted in accordance with ASTM E119, is applied to the connection and the structural members. Results show deflection, rotations, and distortion fields of the structural components for both conventional and new fire resisting steel. Mechanical and thermal plastic strain and stress fields are predicted, documenting yielding, plasticity and ultimate failure in the plate, bolts and structural members. This is a 3D nonlinear model that provides graphical and empirical results for a variety of steel connections that could be used for comparison with established experimental results if available. Design recommendations, failure limitations, and material selection and specifications can be suggested for steel connections in such fire loading.

EVALUATION OF CPT METHODS FOR LOAD AND RESISTANCE FACTOR DESIGN OF DRIVEN PILES

This paper presents an evaluation of eight cone penetration test (CPT) methods and the static method to determine the load and resistance factor design (LRFD) input parameters for single driven piles. Evaluation of these methods was conducted based on load test database of thirty-four square precast prestressed concrete (PPC) driven friction piles tested to failure. Resistance factors for the investigated CPT methods and the static method were determined using reliability-based analysis. Other design input parameters were determined based on the AASHTO LRFD design specifications for bridge substructure. Based on the results of the analysis, the Penpile method showed the highest values of resistance factors while Tumay and Fakhroo and Schmertmann methods showed the lowest values of resistance factors.

Design of steel connections for tie forces

Structural integrity has been required by ASCE 7 for many years but there has not been a specific criterion as to how this requirement could be met. IBC 2009 now contains a structural integrity requirement that applies to high rise buildings assigned to Occupancy Category III or IV . ASCE 7–10 will also have revised integrity requirements International Overview: The UK standards have specific rules for steel structures that were incorporated decades ago as a response to the Government directive that buildings must be resistant to Disproportionate Collapse. Similar rules have now been incorporated into the Eurocodes. This paper highlights the differences between the European and IBC requirements and also discusses the UFC requirements relative to the IBC and ASCE 7. Design Example: The 2009 IBC, Section 1614.3.2, requires that each beam connection have a minimum horizontal tension capacity and also that each column splice have a minimum vertical tension capacity. These requirements are not specifically intended to prevent disproportionate collapse like the UK standards but rather as the section title states, are minimum integrity requirements. This paper provides a discussion of the intent of this section and identifies the specific IBC and ASCE 7 requirements and their implications to steel structures. Tie-force requirements are new in US building codes and hence there is a need to understand the implications that these requirements have to steel design and detailing. This paper presents the historic background and structural intent of tie-forces—both within the US and internationally—and presents specific examples of how to design steel connections to meet the tie-force requirements and compares these requirements to those used in the UK.

Dynamic Response of a Four-Cylinder Compressor Foundation Considering the Effect of Soil-Foundation Interaction—A Case Study

The dynamic response of machine foundation system depends on several factors such as (1) the soil dynamic properties, (2) the geometric properties of the foundation, (3) the amplitude of the applied dynamic loads, and (4) the frequency of the exciting dynamic force. The main goal of machine foundation design is to keep the foundation response within a specific limit of response in order to enable a satisfactory operation of the machine. If the foundation response exceeds this limit, the foundation will adversely affect the performance of the machine and may damage the machine internals, or cause it not to function properly. Furthermore, the excessive vibrations will impose additional stresses on the machine resulting in an increased unbalance loading and thus leading to increased dynamic loads on the soil-foundation system. This paper presents the results of the dynamic analysis of a four-cylinder compressor foundation. The original design of the foundation was performed in the early 1960s and ignored the effect of the soil in the response of the foundation system, thus, the foundation has been suffering from excessive vibration. The foundation block supports a four-cylinder dress-rand compressor, suction and discharge bottles, a crank and driving motor with a total weight of approximately 219 kips. The results of a threedimensional finite element model of the soil–foundation system were used to determine the dynamic response of the soil-foundation system and to assess the foundation response under the applied dynamic loading imposed by the compressor crank. The dynamic analysis is performed by: (1) performing eigenvalue analysis of the foundation block, considering the effect of the soilfoundation interaction to determine the soil-foundation natural frequencies and modal participation factors, and (2) performing forced response of the foundation under applied crankshaft unbalance load to determine the forced response amplitude of the soil-foundation system.

Direct Design Method and Design Diagram for Reinforced Concrete Columns and Shear Walls

Design of reinforced concrete columns and shear walls is an iterative process. Whether done manually or computer aided, the capacity of an assumed section is checked using interaction diagrams and the procedure continues until a satisfactory section is found. This research introduces two new concepts for design of reinforced concrete columns, “Direct Design” method and “Design Diagram”. Direct design method is an analytical approach by which the required area of reinforcement is determined directly without using an interaction diagram. In this approach, location of the neutral axis and required area of reinforcement is found directly by solving a non-linear system of equations. Direct design method provides an optimum solution for a reinforced concrete section; the capacity of the section is exactly equal to the applied load and moments. For each column or shear wall, there are many optimum sections with different sizes and bar arrangements. A design diagram shows all possible optimum sections for a column or shear wall. This study provides an algorithm and a computer program for making design diagrams. Having a design diagram, designers do not need to go through a trial-and-error procedure to find an acceptable section; they can simply pick up an optimum section that best fits their requirements from the design diagram.

Finite element analysis of tension-loaded ASTM A325 bolts under simulated fire loading

Purpose Nuts and bolts have been used as fasteners of steel structures for many years. However, these structures remain susceptible to fire damage. While conducting fire experiments on steel structures is sometimes necessary, to better understand their behavior, such experiments remain costly and require specialized equipment and testing facilities. This paper aims to present a highly accurate three-dimensional (3D) finite element (FE) model of ASTM A325 bolt subjected to tension loading under simulated fire conditions. The FE model is compared to the results of experimental testing for verification purposes and is proven to predict the response of similar bolts up to certain temperatures without the need for repeated testing. Design/methodology/approach A parametric 3D FE model simulating tested specimens was constructed in the ANSYS Workbench environment. The model included the intricate details of the bolt and nut threads, as well as all the other components of the specimens. A pretension load, a tension force and a heat profile were applied to the model, and a nonlinear analysis was performed to simulate the experiments. Findings The results of the FE model were in good agreement with the experimental results, deviations of results between experimental and FE results were within acceptable range. This should allow studying the behavior of structural bolts without the need for expensive testing. Originality/value Detailed 3D FE models have been created by the authors have been created to study the behavior of structural bolts and compared with experiments conducted by the authors.

Behavior of ASTM A325 bolts under simulated fire conditions: experimental investigation

Purpose Heavy hex structural bolts have been used in a wide range of steel structures for many years. However, these structures remain susceptible to fire damage. Conducting fire experiments on full-scale steel structures is costly and requires specialized equipment. The main purpose of this research is to test, analyze and predict the behavior of ASTM A325 bolts under tension loading in simulated fire conditions and develop a reliable finite element model that can predict the response of similar bolts without the need for repeated testing. Design/methodology/approach The experimental work was conducted at the University of Wisconsin-Milwaukee, where an electric furnace was custom-built to test a bolted specimen in tension under elevated temperatures. A transient-state testing method was adopted to perform a group of tests on 12.7 mm (½”) – diameter A325 bolts. The tests were divided into two groups: the first one was used to calibrate the equipment and choose a final testing arrangement and the second group, consisting of four identical tests, was used to validate a finite element model. Findings The temperature-displacement and load-displacement response was recorded. The tested bolts exhibited a ductile fracture in which a cup-and-cone shaped failure surface was formed in the threaded section at the root of the nut. ASTM A325 bolts are widely used by engineers in building and bridge construction, the results of this research enable engineers to determine the behavior and strength of ASTM A325 bolts when such bolts when exposed to fire event. Research limitations/implications Structural bolts are used to connect structural members, and they are part of structural assembly. To study the behavior of the bolts, the bolts only were investigated in a fire simulated in a furnace. The bolts studied were not part of a structural assembly. Practical implications The results of this study enable engineers to evaluate the condition of ASTM A325 bolts when subjected to fire loading. Originality value Tests were conducted at the University of Wisconsin – Milwaukee’s structures laboratory to study the effect of fire on an ASTM A325 bolts. Many tests under fire loading have been performed by researchers on different components of steel structures, this study focuses on studying the behavior of ASTM A325 bolts which are widely used in the USA.

Behavior of Skewed Extended Shear Tab Connections

This study aims to investigate the skewed extended shear tab connections’ behavior. In order to achieve the goal of the study, finite element models for orthogonal configuration were generated using the finite element analysis software ABAQUS. Results were compared with their counterparts obtained from experimental testing to verify the finite element models. Then, finite element models were skewed at different angles, results obtained from skewed configuration were compared with orthogonal results. It was observed that the skewed and the orthogonal configurations have the same failure models, however, the twist of the shear plate increases with increase of the connection’s orientation due to the additional twisting moment transferred from the supported beam to the supporting member. Additionally, it was found that the connection’s vertical displacement is independent from the connection’s orientation. The relationship between the connection’s twist and the skewed angle was investigated, it was observed that this relationship can be represented using a linear equation. This equation was utilized to derive an equation that relates the skewed and orthogonal connection’s twist. The proposed equation can be used to modify the plate required shear strength and the plate torsional strength equations in the AISC manual 14 th edition in order to determine the need for stabilizer plates.