Multi-objective optimal seismic design of buildings using advanced engineering materials

Although seismic safety remains a major concern of society--and unfortunately this observation has been underpinned by recent earthquakes--economy and sustainability in seismic design are growing issues that the engineering community must face due to increasing human population and excessive use of the earth???s nonrenewable resources. Previous studies have addressed the design and assessment of buildings under seismic loading considering a single objective, namely, safety. Seismic design codes and regulations also center on this objective. The goal of this study is to develop a framework that concurrently addresses the societal-level objectives of safety, economy and sustainability using consistent tools at every component of the analysis. To this end, a high-performance material; namely, engineered cementitious composites (ECC) is utilized. ECC is classified under the general class of fiber-reinforced concrete (FRC); however, ECC is superior to conventional FRC in many aspects, but most importantly in its properties of energy absorption, shear resistance and damage tolerance, all of which are utilized in the proposed procedure. The behavior of ECC is characterized through an experimental program at the small-scale (scale factor equal to 1/8). Numerical modeling of ECC is also performed to carry out structural level simulations to complement the experimental data. A constitutive model is developed for ECC and validated at the material, component and system levels. Additionally, a parametric study of ECC columns is performed to investigate the effect of material tensile properties on the structural level response metrics. Reducing the LCC of buildings (through reductions in material usage and seismic damage cost) is required to achieve the objectives of economy and sustainability. A rigorous LCC formulation that uses advanced analysis for structural assessment, and that takes into account all sources of uncertainty, is used along with an efficient search algorithm to compare the optimal design solutions. A novel aspect of this work is that three different structural frames are considered, RC, ECC and a multi-material frame in which ECC is deployed only at the critical locations (e.g. plastic hinges) to improve seismic performance. By considering the inelastic behavior of structures and incorporating all the required components, the proposed framework is generic and applicable to other types of construction such as bridges, to other innovative materials such as high performance steels, and to other extreme loading scenarios such as wind and blast.unpublishednot peer reviewe

Impact of New Madrid Seismic Zone Earthquakes on the Central USA, Vol. 1 and 2

The information presented in this report has been developed to support the Catastrophic Earthquake Planning Scenario workshops held by the Federal Emergency Management Agency. Four FEMA Regions (Regions IV, V, VI and VII) were involved in the New Madrid Seismic Zone (NMSZ) scenario workshops. The four FEMA Regions include eight states, namely Illinois, Indiana, Kentucky, Tennessee, Alabama, Mississippi, Arkansas and Missouri. The earthquake impact assessment presented hereafter employs an analysis methodology comprising three major components: hazard, inventory and fragility (or vulnerability). The hazard characterizes not only the shaking of the ground but also the consequential transient and permanent deformation of the ground due to strong ground shaking as well as fire and flooding. The inventory comprises all assets in a specific region, including the built environment and population data. Fragility or vulnerability functions relate the severity of shaking to the likelihood of reaching or exceeding damage states (light, moderate, extensive and near-collapse, for example). Social impact models are also included and employ physical infrastructure damage results to estimate the effects on exposed communities. Whereas the modeling software packages used (HAZUS MR3; FEMA, 2008; and MAEviz, Mid-America Earthquake Center, 2008) provide default values for all of the above, most of these default values were replaced by components of traceable provenance and higher reliability than the default data, as described below. The hazard employed in this investigation includes ground shaking for a single scenario event representing the rupture of all three New Madrid fault segments. The NMSZ consists of three fault segments: the northeast segment, the reelfoot thrust or central segment, and the southwest segment. Each segment is assumed to generate a deterministic magnitude 7.7 (Mw7.7) earthquake caused by a rupture over the entire length of the segment. US Geological Survey (USGS) approved the employed magnitude and hazard approach. The combined rupture of all three segments simultaneously is designed to approximate the sequential rupture of all three segments over time. The magnitude of Mw7.7 is retained for the combined rupture. Full liquefaction susceptibility maps for the entire region have been developed and are used in this study. Inventory is enhanced through the use of the Homeland Security Infrastructure Program (HSIP) 2007 and 2008 Gold Datasets (NGA Office of America, 2007). These datasets contain various types of critical infrastructure that are key inventory components for earthquake impact assessment. Transportation and utility facility inventories are improved while regional natural gas and oil pipelines are added to the inventory, alongside high potential loss facility inventories. The National Bridge Inventory (NBI, 2008) and other state and independent data sources are utilized to improve the inventory. New fragility functions derived by the MAE Center are employed in this study for both buildings and bridges providing more regionally-applicable estimations of damage for these infrastructure components. Default fragility values are used to determine damage likelihoods for all other infrastructure components. The study reports new analysis using MAE Center-developed transportation network flow models that estimate changes in traffic flow and travel time due to earthquake damage. Utility network modeling was also undertaken to provide damage estimates for facilities and pipelines. An approximate flood risk model was assembled to identify areas that are likely to be flooded as a result of dam or levee failure. Social vulnerability identifies portions of the eight-state study region that are especially vulnerable due to various factors such as age, income, disability, and language proficiency. Social impact models include estimates of displaced and shelter-seeking populations as well as commodities and medical requirements. Lastly, search and rescue requirements quantify the number of teams and personnel required to clear debris and search for trapped victims. The results indicate that Tennessee, Arkansas, and Missouri are most severely impacted. Illinois and Kentucky are also impacted, though not as severely as the previous three states. Nearly 715,000 buildings are damaged in the eight-state study region. About 42,000 search and rescue personnel working in 1,500 teams are required to respond to the earthquakes. Damage to critical infrastructure (essential facilities, transportation and utility lifelines) is substantial in the 140 impacted counties near the rupture zone, including 3,500 damaged bridges and nearly 425,000 breaks and leaks to both local and interstate pipelines. Approximately 2.6 million households are without power after the earthquake. Nearly 86,000 injuries and fatalities result from damage to infrastructure. Nearly 130 hospitals are damaged and most are located in the impacted counties near the rupture zone. There is extensive damage and substantial travel delays in both Memphis, Tennessee, and St. Louis, Missouri, thus hampering search and rescue as well as evacuation. Moreover roughly 15 major bridges are unusable. Three days after the earthquake, 7.2 million people are still displaced and 2 million people seek temporary shelter. Direct economic losses for the eight states total nearly $300 billion, while indirect losses may be at least twice this amount. The contents of this report provide the various assumptions used to arrive at the impact estimates, detailed background on the above quantitative consequences, and a breakdown of the figures per sector at the FEMA region and state levels. The information is presented in a manner suitable for personnel and agencies responsible for establishing response plans based on likely impacts of plausible earthquakes in the central USA.Armu W0132T-06-02unpublishednot peer reviewe

Leadership and Legacy: A History of Civil and Environmental Engineering at Illinois

William J. Hall Professor Emeritus By virtue of many factors, including increasing inquiries as to the history of the department, it was decided it was time to assemble existing documents into one succinct booklet. We begin with a piece on civil engineering education, a statement by the current department head about major thrusts that will guide the department's initiatives into the future, and a brief overview of the department, followed by a history of the department. Finally, we end with some miscellaneous information of interest.Ope

Design and assessment spectra for retrofitting of RC buildings

This article presents a novel approach for deriving Retrofit Design Spectra (RDS) that are intended for use in preliminary development and assessment of seismic upgrading scenarios of existing structures. The new spectral representation relates the characteristics of the intervention method chosen as the core of the upgrading strategy, with the ductility and strength demand of the retrofitted structure. The methodology utilized for the derivation of the RDS is based on the Capacity Spectrum Method where the capacity curve is described by relationships for global and local intervention methods that are parameterized in terms of fundamental response quantities. The proposed spectra provide direct insight into the complex interrelation between the characteristics of the intervention method and the implications of the upgrading scenario on demand. Alternative retrofit solutions are thus assessed in an efficient way. A case study is used to illustrate practical application of the new approach

Seismic Retrofitting of Steel and Composite Building Structures

This report provides criteria to evaluate the performance of existing buildings with steel and composite structures, either framed or braced. It also presents a comprehensive review of rehabilitation strategies to retrofit structural members and connections (local intervention) and/or frames (global intervention). The evaluation criteria and upgrade schemes have been derived from extensive experimental and numerical tests carried out in Europe, Japan and the US in the aftermath of recent earthquakes. They are intended to enhance the strength, stiffness and energy dissipation of existing framed buildings during future earthquakes. Indeed, it is expected that retrofitted buildings exhibit: (i) no damage during low-intensity earthquakes, (ii) some nonstructural damage during moderate earthquakes and (iii) structural and nonstructural damage during major events but the global collapse is prevented.National Science Foundation EEC-970178

Assessment of Seismic Integrity of Multi-Span Curved Bridges in Mid-America

The study presents a detailed seismic performance assessment of a complex office-designed bridge using state-of-the-art assessment tools and metrics. The impact of design assumptions on the capacity estimates and dynamic characteristics of a multi-span curved bridge are investigated. A single nine-span bridge is studied whilst the level of attention to detail is significantly higher than can be achieved in a mass parametric study of a population of bridges. The objective is achieved by in-depth investigation of the bridge representing the ???as-designed??? (including features assumed in the design process) and that representing the ???as-built??? (actual expected characteristics) structure. Three-dimensional detailed dynamic response simulations of the investigated bridge including soil-structure interaction effects are undertaken. The behavior of the ???as-designed??? bridge is investigated on two different analytical platforms for elastic and inelastic analysis. A third idealization is adopted to investigate the ???as-built??? behavior by realistically modeling bridge bearings, structural gaps and materials. A comprehensive list of local and global, action and deformation, performance indicators are selected to monitor the response to earthquake action, including bearing slippage and segment collision. The adopted methodology and results of elastic and inelastic analyses are discussed. The comparative study has indicated that the lateral capacity and dynamic characteristics of the as-designed bridge are significantly different than the as-built behavior. The potential of pushover analysis in identifying structural deficiencies, estimation of capacities and providing insight into the pertinent limit state criteria are demonstrated. The conclusions from this study are important for designers and assessors of the seismic response of complex bridges since it highlights potentially non-conservative assumptions that are frequently used in the design office.NSF Grant EEC-9701785published or submitted for publicatio

Seismic Vulnerability of Flat-Slab Structures

The study has three main objectives. The first objective is to investigate the fragility of flat-slab reinforced concrete systems. Developing the fragility information of flat-slab construction will be a novel achievement since the issue has not been the concern of any research in the literature. The second objective is to assess HAZUS as an open-source, nationally accepted earthquake loss estimation software environment. It is important to understand the potentials and the limitations of the methodology, the relationship between the hazard, damage and the loss modules, and the plausibility of the results before using it for the purposes of hazard mitigation, preparedness or recovery. The last objective is to implement the fragility information obtained for the flat-slab structural system into HAZUS. The methodology involves many built-in specific building types, but does not include flat-slab structures. Hence it will be extra achievement to develop HAZUScompatible fragility curves to be used within the methodology.National Science Foundation EEC-970178

Analytical Assessment of an Irregular RD Full Scale 3D Test Structure

The advancement of seismic assessment of structures depends on three main ingredients, namely advanced and well-controlled testing techniques, accurate analytical simulations and the existence of measured data for verification. Recent advancements in testing and analysis are welldocumented, and the literature abounds with simulation approaches, both physical and computational. However, real data from the seismic performance of structures of the required characteristics and at the sought after limit states is severely lacking. This is a consequence of the very limited number of full scale tests conducted around the world; such tests are in the range of 10 or so for the wide class of reinforced concrete structures (Rossetto and Elnashai, 2003). With regard to data collected after earthquakes, the quality of observations is subject to the following considerations: a. The number of structures with light damage is significantly larger than the number of cases of partial and total collapse. Therefore, the statistical viability of the latter is at best questionable. b. It is unlikely that the building stock subjected to earthquake motion is that which is being investigated by researchers; i.e. work on dual frame-wall structures require data on seismic response of the same system, preferably designed to the same criteria. c. Design and construction practices are regional, hence damage data from one region may not be transferable due to ???supply incompatibilities???. d. Ground motion characteristics are also regional thus limiting the transferability of damage data due to ???demand incompatibility???. The above discussion lends weight to allocating resources to full scale testing as possibly the most promising and controlled means of obtaining structural performance data under earthquake loading for the verification of structural systems, the further development of testing procedures and the calibration of analytical models. In this context, a full scale test of a 3 story 2??2 bays irregular reinforced concrete structure was carried out at the European Laboratory for Structural Assessment (ELSA) of the Joint Research Center (JRC) in Ispra, Italy, under the auspices of the EU project Seismic Performance Assessment and Rehabilitation (SPEAR). As part of the aforementioned project, this report presents detailed seismic assessment of the building and pretest. The main objectives are to aid in refining the test details, defining the sequence of testing, selecting the most suitable input motion record and the intensity that will cause the structure to reach the desired limit state. Numerical simulations are performed for pre-test condition assessment of the specimen, estimation of the actuator motion during the test and determination of the weight locations. Below, full structure-, story- and member-level seismic assessment of the test model is described. Pre-test models with different assumptions are presented and their analysis results are compared with the experimental result.unpublishe

Probabilistic Seismic Assessment of Structure, Foundation and Soil Interacting Systems

This report presents research on the probabilistic seismic performance evaluation of a structural-geotechnical interacting system. The system comprises a bridge, its foundation, and the supporting soil. The investigation includes a study on probabilistic performance evaluation methodologies, development of a multiplatform and hybrid simulation framework, verifications of numerical models of structural and geotechnical systems in comparison with measured data, and the derivation of fragility curves of a bridge in Central and Eastern United States. Seismic performance evaluation procedures are studied using a benchmark threestory, reinforced concrete (RC) building structure. Three probabilistic performance evaluation methods are applied: the Monte Carlo simulation, response surface, and SACFEMA methods. The analysis of benchmark structure shows that the effect of random variability in structural materials is small compared to the effect of input ground motion. When Peak Ground Acceleration (PGA) is used as an intensity measure, the derived vulnerability curves highly depend on ground motion sets. Three different simulation methods results in similar vulnerability curves. The computational cost are the most expensive when the Monte Carlo simulation is adopted. Methodologies for soil-structure-interaction analysis are introduced, including the newly developed multiplatform, multiresolution hybrid simulation framework. These methodologies and numerical models of soil-structure-interaction systems are verified through comparison with field measurements and experimental results. The soil-structure interacting system is verified through analyses of a heavily instrumented bridge which recorded several sets of ground motions. The verification study of soil-structure interacting system shows that detailed and meticulously developed analytical models are capable of replicating measurements of the response of complex bridge systems subjected to strong ground motion. Seismic vulnerability curves of a reference bridge in the Central and Eastern United States (CEUS) are derived employing the aforementioned methods with and without soilstructure interaction. A typical highway over-crossing bridge representing one of the most common bridge types in the CEUS is selected. Four different approaches of Soil- Structure Interaction (SSI) are tried: (a) Abutments and foundations are assumed to be fixed, (b) Conventional lumped spring approaches are adopted to model abutments and foundations, (c) Lumped springs for abutments and foundations are estimated from Finite Element (FE) analysis of geotechnical system, and (d) Multiplatform simulation is conducted. All four of the methods shows that abutment bearings in transverse direction are most vulnerable components. Failure probability of the bridge system is highly dependent on the failure probability of abutment bearings. Considering that simplified methods for SSI analysis include larger assumptions than fully coupled methods and that the multiplatform simulation is verified with measured responses from instrumented bridge, the use of multiplatform simulation is suggested if computational power and resources for FE modeling are affordable.published or submitted for publicatio

Seismic Response of RC Members Subjected to the 2009 L'Aquila (Italy) Near-Field Earthquake Ground Motions

The present work assesses the seismic response of reinforced concrete (RC) members subjected to horizontal (HGMs) and vertical (VGMs) ground motions recorded during the 2009 L???Aquila (Italy) earthquake. Normalized axial loads in beam-columns as well as the peak ground acceleration ratios between horizontal and vertical ground accelerations are emphasised as they are considered parameters of paramount importance for the assessment of structural components and systems subjected to combined horizontal and vertical ground motions (HVGMs). Results of extensive parametric nonlinear dynamic analyses carried out on simplified structural models are discussed in detail. The sample models comprise cantilever RC columns and a two-storey, two-bay plane frame designed for gravity loads. The response quantities for the performed analyses are expressed in terms of axial loads, axial deformations, bending moment-axial load interaction and shear demand/capacity ratios. It is found that the variation of axial loads is significant in columns under HVGMs, especially in compression. For values of normalized axial loads (v) corresponding to actual RC columns in framed building structures, e.g., normalized axial load v>0.10, the average increase of the compression load ranges between 174% (v=0.20) and 59% (v=0.50). For high values of normalized axial loads the computed axial load-bending moment pairs lie beyond the threshold interaction curves and, in turn, the RC members fail. The shear demand-to-supply ratio is also detrimentally affected by the high fluctuations of axial loads in the columns. Net tensile forces were computed for columns with low-to-moderate axial gravity preload. In multi-storey framed buildings, the response of central columns is significantly affected by the HVGMs. Reliable seismic performance assessment of framed systems requires that combined HGMs and VGMs should be accounted for in the analyses.unpublishednot peer reviewe