Bora Gencturk

Further development of matrix-based system reliability method and applications to structural systems

In efforts to estimate the risk and reliability of a complex structure or infrastructure network, it is often required to evaluate the probability of a ‘system’ event, i.e. a logical function of multiple component events. Its sensitivities with respect to design parameters are also useful in decision-making processes for more reliable systems and in reliability-based design optimisation. The recently developed, matrix-based system reliability (MSR) method can compute the probabilities of general system events including series, parallel, cut-set and link-set systems, and their parameter sensitivities, by use of efficient matrix-based procedures. When the component events are statistically dependent, the method transforms the problem into an integral in the space of random variables which cause the statistical dependence, termed as the common source random variables (CSRVs). One can identify CSRVs by fitting a generalised Dunnett-Sobel (DS) model to a given correlation coefficient matrix. This article introduces two further developments of the MSR method: First, for efficient evaluation, it is proposed that the integral in the CSRV space can be performed using the first- or second-order reliability methods. Second, a new matrix-based procedure is developed to compute the sensitivity of the system failure probability with respect to the parameters that affect the correlation coefficients between the components. In addition, an extensive parametric study is performed to investigate the effect of the error in fitted generalised DS model on the accuracy of the estimates by the MSR method. The further developed MSR method is demonstrated by two examples: system reliability analysis of a three-storey Daniels system structure, and finite element reliability analysis of a bridge pylon system.

Carbonation-Induced and Chloride-Induced Corrosion in Reinforced Concrete Structures

AbstractCorrosion is one of the most critical problems that impair the durability of RC structures. Both carbonation-induced and chloride-induced corrosion widely prevail in civil infrastructure around the globe. Expansive products are formed due to corrosion at the interface between concrete and reinforcing bar (rebar). The cracking and spalling in concrete due to expanding corrosion products and the reduction in the cross-sectional area of rebar jeopardize the safety and serviceability of RC structures. From an outsider perspective, this literature review summarizes the state of the art on the mechanisms of the two types of corrosion, mechanical degradation in RC structures as a result of these mechanisms, the analytical methods to predict the basic parameters most related to corrosion, and the available laboratory and field corrosion measurement techniques.

Simulation-Based Fragility Relationships for Unreinforced Masonry Buildings

Unreinforced masonry (URM) structures represent a significant portion of the residential building stock of the central and eastern United States. Fifteen percent of homes in the eight-state region impacted by the New Madrid Seismic Zone are URM buildings. The brittle nature of URM buildings further supports a thorough consideration of seismic response given the susceptibility to severe failure modes. Cur- rently, there is a pressing need for analytically based fragility curves for URM buildings. To improve the estimation of damage-state probabil- ities through the development of simulation-based URM fragilities, an extensive literature survey is conducted on pushover analysis. Using these data, capacity curves are generated, from which damage performance limit states are defined. Demand is simulated using synthetically derivedaccelerogramsrepresentativeofthecentralandeasternUnitedStates.Structuralresponseisevaluatedusinganadvancedcapacityspec- trum method. Capacity, demand, and response are thus derived analytically and utilized to generate a more reliable and uniform set of fragility curves for use in loss-assessment software. This paper presents a framework amenable to rapid, flexible updating that, with the appropriate database of studies, is capable of producing curves representative of any URM building typology subjected to a specified hazard. The curves are expressed in multiple forms to demonstrate capability of use in various loss-assessment applications. DOI: 10.1061/(ASCE)ST.1943- 541X.0000648.

Life-Cycle Environmental Impact Assessment of Reinforced Concrete Buildings Subjected to Natural Hazards

AbstractWith the occurrence of devastating natural disasters worldwide, even though initially used interchangeably with green or environmental development, sustainability has evolved to possess social and economic implications as well. Therefore, a complete sustainability assessment of any civil infrastructure requires an evaluation of its three major components: cost, and environmental and social impacts. Because the construction industry is a pioneer in the sustainability movement, the civil engineering community at large needs an integrated methodology for conducting sustainability assessment of civil infrastructure. This paper focuses on the environmental impact assessment component of sustainability within a comprehensive framework for conducting a life-cycle assessment of structures subjected to natural hazards. Although environmental emissions and waste generation in the initial manufacturing and construction phases make significant contributions to the total environmental impact, long-term structu...

An experimental investigation of innovative bridge columns with engineered cementitious composites and Cu?Al?Mn super-elastic alloys

Recent strong earthquakes have shown that reinforced concrete (RC) bridge columns constructed using conventional materials and techniques suffer from major damage and permanent deformations. The yielding of the longitudinal reinforcement as the main source of energy absorption, and cracking and spalling of concrete results in a dysfunctional bridge structure that does not support the post-disaster recovery efforts. This paper investigates the use of engineered cementitious composites (ECCs) and Cu–Al–Mn super-elastic alloys (SEAs) to improve the performance of bridge columns under seismic loads. A new column design is proposed, which is composed of a pre-fabricated ECC tube that encompasses the longitudinal and transverse steel reinforcement (rebar). The rebar in the plastic hinge region of the cantilever columns was totally or partially replaced with Cu–Al–Mn SEA bars. The tube was filled with conventional concrete after it was placed inside the rebar cage of the foundation. ECC exhibits superior tensile ductility, bonding with steel, energy absorption and shear resistance, in addition to lower permeability and reduced crack widths compared to conventional concrete. Cu–Al–Mn SEA bars are capable of recovering large inelastic deformations exceeding 12% strain. The proposed approach capitalizes on the deformability of ECC with reduced damage, and the energy absorption capacity of Cu–Al–Mn SEA bars without permanent deformation. A total of six column specimens were constructed and tested under simulated seismic loading. The number of rebars replaced with Cu–Al–Mn SEA bars, ECC mixture design, and the ratio of the concrete core area to total column cross-sectional area were the variables investigated in the test program. A comparison of the results indicated that the proposed concept with no Cu–Al–Mn SEA bars provides higher lateral strength, similar energy absorption and reduced damage compared to conventional RC columns; however, similar to a conventional column, it results in excessive permanent deformations. Using Cu–Al–Mn SEA bars in the proposed concept led to a lower lateral strength and energy absorption while the permanent deformations were reduced significantly (over 90%).

Behavior of Concrete and ECC Structures under Simulated Earthquake Motion

AbstractThe objective of the research presented in this paper is to investigate, experimentally, the effect of material- and section-level parameters on the structural response of concrete and engineered cementitious composite (ECC) buildings. In addition to testing of columns under monotonic, cyclic, and static-time history loading, hybrid simulation of structural frames is conducted. Stiffness, strength, ductility, and energy absorption capacity are selected as the response measures that represent the behavior of structures under seismic actions. The investigated variables are reinforcement ratios, ECC material properties, and axial load levels. The results are proposed as basic guidelines to determine the performance enhancement in terms of stiffness, strength, ductility, and energy absorption capacity, which could be achieved by replacing concrete with the high-performance material ECC.

Fragility Relationships for Populations of Woodframe Structures Based on Inelastic Response

In the absence of comprehensive and statistically viable observational damage data, there is a pressing need for simulation-based fragility relationships for populations of structures so as to improve the reliability of earthquake loss assessment studies. In this article, improved fragility relationships for woodframe structures are developed based on inelastic response. Capacity curves are obtained from detailed finite element models, demand is simulated by synthetically generated earthquake ground motions representing a probable earthquake in the Central USA, and structural assessment is carried out using an advanced capacity spectrum method (CSM) presented elsewhere. Thus, all the required components of fragility analysis—namely, capacity, demand, and structural response—are founded on simulated (analytical) behavior. Building classification of the HAZUS loss assessment software is adopted and both HAZUS-compatible and conventional fragility relationships are derived for two different soil conditions. Comparisons with HAZUS fragility curves are given. The parameters of the improved fragility relationships are provided for reliable use in loss assessment software.

Optimal Design of RC Frames Using Nonlinear Inelastic Analysis

Recent earthquakes, especially those in Chile (2010) and Christchurch (2011), have demonstrated the unexpected performance of buildings designed according modern seismic design codes. These incidents strengthen the cause for moving towards performance-based design codes rather than serviceability and strength design. This chapter deals with optimal design of RC frames, a widely used structural type around the world, considering both the initial cost and structural performance as problem objectives. Initial cost comprises the total cost of materials and workmanship for structural components, while structural performance is measured by a two-level approach. First, each design is checked for acceptability according to existing codes, and next performance is quantified in terms of maximum interstory drift obtained from nonlinear inelastic dynamic analysis. This multi-objective, multi-level approach allows one to investigate the implications of the selection of design parameters on the seismic performance while minimizing the initial cost and satisfying the design criteria. The results suggest that structural performance varies significantly within the acceptable limits of design codes and lower initial cost could be achieved for similar structural performance.

Assessment of Stone Arch Bridges under Static Loading Using Analytical Techniques

In this paper the maximum load carrying capacity of masonry arch bridges are assessed. Particularly, stone bridges under investigation have a perfect semicircular geometry and no binding material is used between voussoirs. Analytical methods adopted in this study are the method of virtual work and the mechanism method. In both cases the maximum concentrated load that the bridge can withstand is obtained. Drawing thrust lines for stone arches has a key role in the methods used. Additionally the concept of geometrical factor of safety is also addressed. As a case study, the first century A.D. Roman arch bridge; namely the Titus Tunnel Bridge, is investigated using the methods developed. CE Database subject headings: Stone arches, masonry bridges, mechanism method, thrust lines, geometrical factor of safety, Titus Tunnel Bridge, geometrical nonlinearity.

Reversed Cyclic Behavior of Column-to-Foundation Connections in Low-Rise Metal Buildings

AbstractLow-rise metal buildings constitute a large portion of the nonresidential construction in the United States. These buildings are, in most cases, characterized by a pinned column-to-foundati...