Edward H. Wang

Optimizing Bridge Seismic Retrofit Strategy Implementing Bridge Fragility Curves

Whether an old bridge needs to be brought up-to-date on the seismic design provision, or it deteriorates below the seismic resistant demand it requires a seismic retrofit. A bridge seismic retrofit project often costs a lot and yet the price and the effect of the retrofit are not always proportional. Bridge owners are less likely to experience obvious cases such as described in the Federal Highway Administration Report that once the rehabilitation cost for a given structure begins to exceed 60 percent of the cost of a new structure, the economics begin to favor a replacement. Most of the time, it is ambiguous to owners as to what extend does the retrofit become less cost-effective if the cost of the retrofit does not exceed 60 percent of the cost of a new structure. The aim of this paper is to present a generic decision support system for selecting a cost-effective bridge seismic retrofit strategy implementing analytical fragility curves. The seismic vulnerability of bridges is usually expressed in form of fragility curves, which display the conditional probability that the structural demand caused by various levels of ground shaking exceeds the structural capacity defined by a damage state. Empirical fragility curves are usually developed based on the damage reports from past earthquakes, while analytical fragility curves are developed from seismic response analysis of bridge structures. An Economic Index (EI) is proposed to identify the most cost-effective solution when decision-makers face multiple alternatives. Bridge fragility curves corresponding to various cost levels of retrofit are constructed to compare their effectiveness. The proposed methodology provides engineers and owners with a quantifiable solution for selecting retrofit alternatives.

CONFINED CONCRETE COLUMNS SUBJECTED TO AXIAL LOAD, CYCLIC SHEAR, AND CYCLIC FLEXURE--PART I: ANALYTICAL MODELS

This paper, the 1st in a 2-part series, presents several material and structural models for predicting the behavior of circular confined concrete columns subjected to constant axial load, cyclic shear, and flexure. A simplified model is also presented that may be more suitable for design. In part II, experimental verification from tests of cantilever concrete columns confined with fiber-reinforced plastic (FRP) is given. Both the detailed series of models and the simplified model predict experimental results with reasonable accuracy. The detailed models attempt to explain the behavior of circular concrete columns wrapped with FRP using elementary principles of mechanics. Critical predicted behavior includes wrap strains, force-deflection relationships, and failure modes. Analytical results using detailed models together with experimental results presented in Part II are then used to examine the validity of 6 of the assumptions forming the basis of current design procedures for confined concrete columns. Results from this process suggest that the 6 assumptions are not always consistent with the behavior. The detailed model is cumbersome to apply and needs extensive iteration. The simplified model is proposed as the basis of future design procedures.

A Harbor Resonance Numerical Model with Reflecting, Absorbing and Transmitting Boundaries

Objective: To calculate wave response in an offshore or coastal harbor of arbitrary shape, this research develops a two-dimensional linear, inviscid, dispersive, hybrid finite element harbor resonance model using conservation of energy approach. Based on the mild-slope wave equation, the numerical model includes wave refraction, diffraction, and reflection. The model also incorporates the effects of variable bathymetry, bottom friction, variable, full or partial absorbing boundaries, and wave transmission through permeable breakwaters.

The Kriging Cloud Computing Framework: Interpolation of Topography by Cloud Computing with the Kriging Algorithm

Spatial information surveyed by photogrammetry, airborne LiDAR and Mobile Measurement System (MMS) above ground level can be analyzed by scientists using standard geostatistical methodologies such as ordinary Kriging and sequential Gaussian simulation to interpolate heterogeneities of profiles from sparse sample data. Proven effective by researchers, the Kriging algorithm model is used by commercial data analysis packages for instant interpolation. However, meaningful and reliable results only come with a comprehensive understanding of the variogram associated with valid mathematical functions. To capture spatial landscape variations from massive sample grids of satellite images, this paper presents a cloud computing-based automation approach to improve topography interpolation by taking advantage of rapid computation speed through an open-source cross platform to enrich internet applications. The research team conducted a pilot test on sand beaches, developed the Kriging Cloud Computing Framework, streamlined the Kriging algorithm, developed Kriging Variogram Data Bank and Parameter Management System, derived cross validation procedures and built in Application Programming Interface, API. This new technology can benefit end users around the world in acquiring of ground profiles and production of Digital Elevation Models (DEMs) while requiring only minimal knowledge of the Kriging Method. This cloud computing system facilitates user data input, parameter selection, fast data analysis and model output. The application of this new framework improves remote sensing technology and GIS applications in a variety of unreachable terrains, such as deserts, swamps, and dense forests.

Assessing the Adequacy of Concrete Mixes Utilizing PCB Powders

Solid waste management is becoming a sustainability issue in highly industrialized societies. Recycling or reuse of solid waste is desirable to reduce the adverse impact of this material. The vast annual production of printed circuit board (PCB) waste in Taiwan creates environmental concerns because of the leaching of toxic chemicals into landfills. This study assessed the feasibility of utilizing resin powder and glass fiber recycled from PCB waste as a partial replacement of fine aggregate (natural river sand) in concrete. It also established a comprehensive test program to promote the use of recycling waste for waste reduction. The crushed powder of PCB mixed with standard mortar in fixed volumetric mix proportion, as sand:cement:water = 2.75:1:0.485 was the control group to test the fresh and hardened properties of the material. The test results of hardened specimen properties showed that the addition of PCB resin powder should be less than 10 %, and the addition level of glass fiber should be less than 2 %. The engineering properties and durability matched those of the cement mortar of the standard control group. Because toxic chemicals released from PCB powder and hardened concretes were found to be less than the tolerance limit in the local ordinances, waste PCB can be used in cement mortar, providing an alternative for recycling industrial waste PCB.

Examining Polymerization of Kaolinitic Concrete Using Scanning Electron Microscopy and Raman Spectroscopy

Geopolymers are environmentally friendly substitutes for Portland cement; in many applications, geopolymers not only reduce greenhouse gas emissions but also are recyclable. The hardening mechanism of geopolymer polymerization differs from that of ordinary Portland cement. In the present research, two methods are used to evaluate the microstructure of this inorganic material. In the first method, complete polymerization was observed by means of scanning electron microscopy (SEM) to reveal the foundations of strength establishment. The SEM results show that the synthesized geopolymer maintained a layer structure of metakaolinite particulates. Therefore, it was thought that the geopolymeric reaction mainly occurred at the surface of microflakes of metakaolinite particulates. In order to further investigate the polymerization process of the material, two Raman spectrum frequency ranges—875 nm and 325 nm—were used in the study because of their capability to characterize the mineral/hydrated phases under a thick post-treatment layer. Also, in order to facilitate quality control of the production and explore the extreme compressive strengths of metakaolin cement, the polymerization mechanism and microstructures of the products were monitored step by step using Raman spectroscopy. The lessons learned in the research program can be used to advance the research methodology needed for further investigation of the strength enhancement of the geopolymer.

Assessing Serviceability Improvement Alternatives of Existing Structures

The aim of this paper is to present a generic decision support system for selecting an optimal repair alternative for aging infrastructure systems considering sustainability. Emphasis is placed on how to properly decide on a mainte- nance, repair, rehabilitation, replacement strategy for deteriorating structures, applying the concept of life-cycle cost analysis. Taking into account the decision timing and repair costs of each alternative, an incremental annual uniform cost (IAUC) method is proposed to compare various levels of repair strategies and to reach a rational decision based on the proposed Economic Index (EI). On the sensitivity study of the model, it is concluded that the discount rate has minor im- pact on the selection and the repair timing is crucial to a successful saving. A priority ranking of repair alternatives can be identified once the deterioration model is defined, and the decision timing and repair cost are input. The proposed meth- odology provides engineers and owners with a quantifiable solution at project level for selecting repair alternatives with very minimal input information required.