Spencer E. Quiel

Closed-Form Procedure for Predicting the Capacity and Demand of Steel Beam-Columns under Fire

During a fire, columns on the perimeter of a building will be subject to moments induced by both a thermal gradient and the restraint of axial expansion by adjacent heated beams, which themselves develop axial load. These members thus act as beam-columns because they are then subject to a combination of axial load plus moment caused by a combination of gravity plus thermal loading. This paper presents a two-pronged procedure to predict the behavior of the perimeter column as a beam-column, considering both the individual member response (including thermal gradients) and the global response (including the interactions of adjacent members). All methods discussed in the paper are closed-form (i.e., they require no iteration) and can therefore be solved by using a spreadsheet or simple mathematical algorithm. The framework is sufficiently simple for use in codified structural-fire design and could be included in a reference of performance-based analysis methods for steel structures. Although this paper specif...

Closed-Form Prediction of the Thermal and Structural Response of a Perimeter Column in a Fire

This paper proposes a simplified closed-form methodology with which to predict the thermal and structural re- sponse of steel perimeter columns in high-rise building frames exposed to fire. Due to their orientation in the building compartment, perimeter columns are heated on three sides and will develop a thermal gradient through their cross- sectional depth. Restraint of the thermal expansion associated with this gradient will cause these members to experience a combination of axial load (P) and bending moment (M), thus acting as beam-columns. At high temperatures, the thru- depth gradient will alter the plastic capacity and mechanical behavior of the perimeter column, leading to plastic P-M be- havior that is not captured under the assumption of uniform cross-sectional temperature. Simplified methodologies are proposed to calculate the following: (1) the thru-depth temperature distribution that develops due to three-sided heating, (2) the gradient-induced changes in plastic capacity, and (3) the gradient-induced changes in demand (i.e. P and M). These methodologies are sufficiently simple for use in code-based design and can be implemented via a spreadsheet because they are closed-form. The individual results of each simple methodology as well as their combination are validated against the results of computational thermal and structural analysis, showing good agreement.

Parameters for Modeling a High-Rise Steel Building Frame Subject to Fire

This paper examines the level of detail and complexity that one needs to incorporate in a computational finite element (FE) model to predict the thermal and structural response of steel high-rise building frames to fire. Comparisons are made between these models in terms of accuracy and efficiency. Performance related to three parameters was examined: (1) the representation of the structural system as a 3-D full frame model versus a 2-D plane-frame model, both of which include the steel frame and the floor slab; (2) the representation of the slab in the 2-D plane frame model; and (3) the effects of modeling the temperature profile of each steel member cross-section as non-uniform (i.e. allowing a thermal gradient to develop) versus uniform. Results indicate that the 2-D plane frame model can be reasonably used in some cases to predict the performance of the perimeter column and floor beams framing into them in a fire-exposed high-rise moment-resisting frame (MRF) with a significant savings in analysis run...

Steel Girder Fracture on Delaware’s I-95 Bridge over the Brandywine River

A significant crack was recently discovered on an I-95 bridge over the Brandywine River in Delaware. The steel girder bridge carries six lanes of traffic just north of downtown Wilmington. The crack was located on the fascia girder at midspan of the bridge’s main span. The entire bottom flange was found to be fractured, with the crack extending upwards to within 0.3 meters of the upper flange. This paper will review the circumstances leading up to the crack, discuss the cause of the crack, review the repair strategy, and summarize the results of load tests performed prior to and during the repair.

Blast-Induced Damage Mapping Framework for Use in Threat-Dependent Progressive Collapse Assessment of Building Frames

AbstractThis paper proposes a methodology for mapping structural damage onto building frames due to exterior blast threats for use in a threat-dependent progressive collapse assessment. The proposed approach contrasts with current practice, which typically relies on a threat-independent approach for progressive collapse analysis. Damage is mapped to the structure based on the calculated response of the discrete structural components (particularly the columns) to a blast-induced pressure time history. Contours of structural damage can then be mapped over the building face for discrete combinations of charges and standoffs. For a prototype reinforced concrete building frame, calculated distributions of damage for conventional explosive threats suggest that the current state-of-practice approach (in which damage is represented with a single column removal) may not constitute a generally conservative strategy for progress collapse-resistant design. The proposed framework can be used to determine standoff dist...

Uniform Pushdown Approach for Quantifying Building-Frame Robustness and the Consequence of Disproportionate Collapse

AbstractThis paper proposes a framework for quantifying the structural robustness of building frames that utilizes a relative numerical interpretation of the strength degradation in response to a damage event. The approach leverages uniform pushdown methods in the context of the current design procedures for resisting progressive and/or disproportionate collapse. The primary metric used to evaluate the structure’s collapse resistance is the magnitude of applied load that the damaged system can support relative to both the design loads and the capacity of the undamaged system. By leveraging several aspects of current alternate path approaches to progressive collapse–resistant design, the framework provides practicing engineers with an accessible tool for evaluating the relative robustness of structural systems. A prototype eight-story, precast/prestressed concrete moment frame system is used as a case study to demonstrate the utility of this procedure. The prototype system is modified to increase its colla...

A Performance-Based Framework for Structural Resilience to Blast-Induced Damage

This paper proposes a framework for establishing quantitative measures and mathematically reproducible definitions of structural resiliency as it pertains to a structures ability to minimize the potential for undesirable response to low-probability-high-consequence events. The resiliency assessment and design process follow a logical progression of steps starting with the characterization of hazards and continuing through analysis simulations, damage modeling, and loss assessment by balancing functional relationships between design tradeoffs and associated consequences. The outcomes of each subprocess are articulated through a series of generalized variables: topology, geometry, damage, and hazard intensity measures. A rigorous probabilistic framework permits consistent characterization of the inherent uncertainties throughout the process. The proposed framework is well suited to support the building design process through stochastic characterization of assessment measures. Using a stepwise approach, the framework facilitates a systemwide method to confront multihazard threat scenarios by establishing functional relationships between the development of appropriate models, design methods, damage acceptance criteria, and tools necessary for implementation. The proposed methodology can be implemented directly for assessment of project-specific performance criteria or can be used as a basis for establishing appropriate performance criteria and provisions to achieve resilient structural solutions at the outset of design.

The Behavior of Steel Perimeter Columns in a Fire

This study investigates the thermal and structural effects of fire protection, the slab, and the connection fixity on the thermal and structural behavior of perimeter columns in a common steel-framed high-rise building exposed to fire. A model is developed based on a tall steel building (of common construction) that was subject to conflagration in the last decade. The progression of the fire from floor to floor as it moved up the building is considered in developing the time-temperature curves for the analyses. Structural analyses therefore consider that some floors are cooling down while others are heating up. Results show that the beams framing into perimeter columns expand significantly and induce large moments in the perimeter columns, which may lead to the development of plastic hinges. The development of many plastic hinges in a frame could lead to overall structural instability. This phenomenon is essentially independent of the beam-to-column connection fixity and the presence/absence of a slab; therefore fire protection designs for perimeter columns should consider the beams framing into them, which are integral to structural stability.

Blast Vulnerability Assessment of Road Tunnels with Reinforced Concrete Liners

Tunnels are a critical component of our transportation infrastructure, and unexpected damage to a tunnel can significantly and adversely impact the functionality of a transportation network. Tunnel systems are vulnerable to potential threats of intentional and accidental blast events because of their relatively unrestricted public access. These events can lead to spalling and breach of the tunnel liner which, depending on the surrounding media, can result in local damage and progressive collapse of the tunnel. Current approaches for evaluating blast-induced damage to a tunnel liner either require significant computational effort or oversimplification such that accurate spatial distributions of damage cannot be obtained. This study presents an effective approach to predict and map the damage to a reinforced concrete liner of a roadway tunnel from various explosive threat sizes and tunnel geometries. A literature review of existing studies is conducted, and potential scenarios of blast events are examined with varying charge position and size. Rectangular, horseshoe, and circular tunnel geometries, each with the same traffic throughput, are evaluated. An efficient analytical approach to determine the spatial distribution of blast-induced spall and breach damage is presented and shows good agreement with numerical models analyzed in LS-DYNA. The proposed approach is then used to examine the relationship between increasing blast hazard intensity and the extent of spall and breach damage. Inflection points in this relationship can be used to identify hazard levels at which a progressive collapse evaluation would be warranted.

Computational Challenges in Real-Time Hybrid Simulation of Tall Buildings under Multiple Natural Hazards

The essence of real-time hybrid simulation (RTHS) is its ability to combine the benefits ofphysical testing with those of computational simulations. Therefore, an understanding of the real-timecomputational issues and challenges is important, especially for RTHS of large systems, in advancingthe state of the art. To this end, RTHS of a 40-story (plus 4 basement stories) tall building havingnonlinear energy dissipation devices for mitigation of multiple natural hazards, including earthquakeand wind events, were conducted at the NHERI Lehigh Experimental Facility. An efficient implementationprocedure of the recently proposed explicit modified KR-a (MKR-a) method was developedfor performing the RTHS. This paper discusses this implementation procedure and the real-time computationalissues and challenges with regard to this implementation procedure. Some results from theRTHS involving earthquake loading are presented to highlight the need for and application of RTHSin performance based design of tall buildings under earthquake hazard.