Civil Engineering

Business stakeholders need to have clear and realistic goals if they want to meet commitments in application development. As a consequence, at early stages they prioritize requirements. However, requirements do change. The effect of change forces the stakeholders to balance alternatives and reprioritize requirements accordingly. In this paper we discuss the problem of priorities to non-functional requirements subjected to change. We, then, propose an approach to help smooth the impact of such changes. Our approach ...

Rework has been a primary cause of cost and schedule overruns in large construction projects. While several research efforts have analyzed the causes and effects of rework and provided guidelines to reduce rework, almost no research exists to analyze the impact of rework timing and quantity on schedule delays and to support decisions on cost effective recovery. This research presents a quantitative mechanism for schedule analysis considering rework. The mechanism has three aspects: (1) a new schedule representation of rework magnitude as negative percentage complete for affected activities, documented on the specific date on which the rework is detected; (2) a modified daily-windows delay analysis to apportion project delays among the responsible parties; and (3) an optimization technique for determining the least costly corrective action strategy that recovers project delays. The proposed approach is applied to a case study to demonstrate its ability to consider rework impact, in combination with other progress events by other project parties. This research offers an innovative quantitative approach to consider rework timing and amount in delay analysis and corrective action optimization.

The non-functional requirements (NFRs) of software systems are well known to add a degree of uncertainty to process of estimating the cost of any project. This paper contributes to the achievement of more precise project size measurement through incorporating NFRs into the functional size quantification process. We report on an initial solution proposed to deal with the problem of quantitatively assessing the NFR modeling process early in the project, and of generating test cases for NFR verification purposes. The NFR framework has been chosen for the integration of NFRs into the requirements modeling process and for their quantitative assessment. Our proposal is based on the functional size measurement method, COSMIC-FFP, adopted in 2003 as the ISO/IEC 19761 standard. Also in this paper, we extend the use of COSMIC-FFP for NFR testing purposes. This is an essential step for improving NFR development and testing effort estimates, and consequently for managing the scope of NFRs. We discuss the merits of the proposed approach and the open questions related to its design.

Non-functional requirements (NFRs) of software systems are a well known source of uncertainty in effort estimation. Yet, quantitatively approaching NFR early in a project is hard. This paper makes a step towards reducing the impact of uncertainty due to NRF. It offers a solution that incorporates NFRs into the functional size quantification process. The merits of our solution are twofold: first, it lets us quantitatively assess the NFR modeling process early in the project, and second, it lets us generate test cases for NFR verification purposes. We ...

In order to meet commitments in software projects, a realistic assessment must be made of project scope. Such an assessment relies on the availability of knowledge on the user-defined project requirements and their effort estimates and priorities, as well as their risk. This knowledge enables analysts, managers and software engineers to identify the most significant requirements from the list of requirements initially defined by the user. In practice, this scope assessment is applied to the Functional Requirements (FRs) provided by users who are unaware of, or ignore, the Non-Functional Requirements (NFRs). This paper presents ongoing research which aims at managing NFRs during the software development process. Establishing the relative priority of each NFR, and obtaining a rough estimate of the effort and risk associated with it, is integral to the software development process and to resource management. Our work extends the taxonomy of the NFR framework by integrating the concept of the "hardgoal". A functional size measure of NFRs is applied to facilitate the effort estimation process. The functional size measurement method we have chosen is COSMIC-FFP, which is theoretically sound and the de facto standard in the software industry.

Analytical parametric study on dynamic characteristics of steel tower of cable-stayed bridges is performed to investigate the individual influence of different design aspects, such as damping mechanism, input ground motion, allowable initial construction imperfections, energy dissipation and tower modal shapes. The results show that the horizontal beam height and length and the low yield energy dissipation system significantly affect tower structural behavior. The initial imperfections within design range have slight detrimental effects on the tower seismic response but these effects grow rapidly beyond the design range. Mass proportional damping leads to overestimate tower axial forces and acceleration response.

Damage of adjacent bridge structures due to relative responses, such as pounding and unseating, have been observed in many earthquakes. The isolators in bridge structures are effective in mitigating the induced seismic forces. However, the deck displacement becomes excessively large when subjected to ground motion with unexpected characteristics. This increases the possibility of pounding; and contributes to the unseating of bridge decks and subsequent collapse. An analytical model of expansion joints, that takes account of the interaction between adjacent bridge segments and the effect of impact and restrainers, is developed and nonlinear time history analyses are performed on a typical isolated multi-span bridge using three standard ground motions. The numerical simulation results show that pounding between adjacent bridge segments could amplify the relative displacement, resulting in the requirement of using an unseating prevention system. Restrainers are substantially effective in reducing the relative opening displacements and impact forces due to pounding at the expansion joints. However, the impact and the stretch of cable restrainers at expansion joints results in a large lateral force transfer from one deck to the other, which, consequently, significantly changes the global response of the participating structural systems. Therefore, it is effective to provide a shock absorber for the mitigation of impact effects between bridge segments or at the restrainers’ ends. The sudden changes of stiffness during poundings can be smoothed by using a natural rubber shock absorber, which prevents, to some extent, the acceleration peaks due to impact. The reaction forces at the pier bases and the pounding forces exerted on the superstructure can be satisfactorily reduced.

Investigations of past and recent earthquake damage have illustrated that the building
structures are vulnerable to severe damage and/or collapse during moderate to strong ground motion. Among the possible structural damages, seismic induced pounding has been commonly observed in several earthquakes. A parametric study on buildings pounding response as well as proper seismic hazard mitigation practice for adjacent buildings is carried out. Three categories of recorded earthquake excitation are used for input. The effect of impact is studied using linear and nonlinear contact force model for different separation distances and compared with nominal model without pounding consideration. Pounding produces acceleration and shear at various story levels that are greater than those obtained from the no pounding case, while the peak drift depends on the input excitation characteristics. Also, increasing gap width is likely to be effective when the separation is sufficiently wide practically to eliminate contact.

Abstract; A nonlinear dynamic analysis program is used to investigate the steel tower of cable-stayed bridges based on total La gian formulation using linearized finite displacement theory and fiber model, where a finite element procedure for the nonlinear dynamic ...

Damages of adjacent bridge structures due to relative responses such as poundings and unseating have been observed in many earthquakes. The isolators in bridge structures are effective in mitigating the induced seismic forces, however, the deck displacement becomes excessively large when subjected to a ground motion with unexpected characteristics, therefore increase the possibility of pounding; contribute to the unseating of bridge decks and subsequent collapse. An analytical model of expansion joints that takes account of the interaction between adjacent segments of the bridge deck and the effect of impact and restrainers is developed for nonlinear time history analysis. The numerical results show that pounding between adjacent bridge segments could amplify the relative displacement, resulting in the requirement of a longer seat width to support the deck. Pounding results in a transfer of large lateral force from a deck to the other, consequently, results in significant changes in the global response of the participating structural systems. So it is effective to provide a shock absorber between adjacent decks for the mitigation of pounding effect.

The problem of soil structure interaction in the seismic analysis and design of long-span bridges in seismically active regions is potentially important to highway facilities design. A quite general nonlinear dynamic soil structure interaction analysis methodology is developed to estimate seismic response characteristics of cable-stayed bridges tower, in which the effect of the soil flexibility underneath the foundation and its associated geometric and hysteretic damping are included. Due to rocking response of a spread foundation under a strong near-field ground motion that may result in the foundation uplift and the yield of the underlying soils, both of strain-dependent material nonlinearity and geometrical nonlinearity by base mat uplift are considered. The soil parameters values that are considered in the design process are used to observe the effect of soil nonlinearities upon the tower-pier seismic response. Numerical results indicate that force response quantities of the physical sub-structure stiffness tower model can be reduced by considering soil foundation interaction and different soil nonlinearities. The soil yielding below the foundation and uplift at the interface have significantly contribution to foundation rocking response. The soil bearing stress beneath the footing base dramatically increases due to footing base uplift. The predominant contribution to the vertical response at footing base comes from the massive foundation rocking rather than from the vertical excitation. The spectrum amplitude at tower top contains only the dominant flexible super-structure frequency and all other frequencies, which present in the massive and rigid sub-structure base level, have been essentially filtered out.

Base connection exhibits the most unpredictable semi-rigid behaviour. Thus, an exact evaluation of the connection response can be achieved through the corresponding analysis of sophisticated three dimensional finite element numerical simulations. As base connection structural characteristic change is manifested in the long term due to deterioration of concrete base and steel anchors, the anchor bolt stiffness and pretension force could decrease, hence lead to extra vertical motion in the base plate and loosing between the base plate and the concrete. This study objective is to investigate the seismic response of steel tower of cable-stayed bridges with base plate lift-off and to find the best way to deal with lift-off of anchor under different input ground motions. A representative problem of a cable-stayed bridge tower is analyzed under two different strong ground motions. The base connection is idealized by a spring system that considers connection expected vertical motion. A finite element methodology based on theoretical approach and computer simulations for nonlinear dynamic analysis problem including base connection modelling is presented. The bearing stress on the concrete foundation and the demand of anchor bolt is computed. From this study finding the base plate lift-off effects are recommended to be incorporated in bridge seismic design in order to take the safety level enhancement.

The traditional approach to seismic hazard mitigation is to design structures with sufficient strength capacity and the ability to deform in a ductile manner. Alternatively, newer concepts of structural control have been growing in acceptance as design alternative for earthquake hazard mitigation. The control systems can be used as base isolators to achieve different objectives or performance goals ranging from a life safety standard to a higher standard that would provide damage control. In this study, an isolated base connection modeling is presented in order to enhance seismic behavior of bridge towers by using viscoelastic material. The material and geometrical nonlinear behavior of the base plate is considered. Nonlinear contact of the bridge towers with the base plate and concrete foundation has been demonstrated and its implementation in a finite element nonlinear analysis is presented. A time domain finite element methodology for nonlinear dynamic analysis problem is developed. That accounts for the isolated bridge towers and the inelastic behavior of base plate through an incremental-iterative procedure. A representative problem of cable-stayed bridge towers subjected to a strong ground motion is analyzed. The study shows how the proposed isolated connection enhances the seismic behavior of the bridge towers.

Special bridges are those curved, skew and long-span bridges; require special considerations in their analysis; design and construction. Typically, these bridges exhibit complex behaviour in which the vertical, lateral, and torsional motions are often strongly coupled that raises many concerns about their behaviour under dynamic loads. Application of passive control devices has been shown to be effective to protect bridges under seismic excitation. The effect of bi-directional seismic excitation is essential for analysis and design of seismically isolated bridges, since the bi-directional motion is coupled and two independent unidirectional models could not accurately describe the bi-directional behaviour. The seismic response of lumped-mass bridge model to bi-directional harmonic and real earthquake ground motions is investigated; the biaxial interaction Bouc-Wen model is used to account for the direction and magnitude of the bearing resultant hysteretic forces, the system response with biaxial interaction is compared with those without interaction. Numerical results show that the isolated bridge is significantly influenced by the interaction of bearing forces.

A quite general base connection modeling capable of accurately representing material and geometrical nonlinear behavior of the base plate and arbitrary nonlinear contact with concrete foundation has been demonstrated and its implementation in a finite element nonlinear seismic analysis is presented. A time domain finite element methodology for nonlinear dynamic analysis problem that accounts for base connection lift-off and the inelastic behavior of anchor bolts through an incremental-iterative procedure is developed. A representative problem of cable-stayed bridges tower subjected to strong ground motion is analyzed. The maximum bearing stress on the concrete foundation as well as the tension force per anchor bolt that necessary to design the anchorage system is computed.

Damages of adjacent bridge structures due to relative responses such as poundings and unseating have been observed in many earthquakes. The isolators in bridge structures are effective in mitigating the induced seismic forces, however, the deck displacement becomes excessively large when subjected to a ground motion with unexpected characteristics, therefore increase the possibility of pounding; contribute to the unseating of bridge decks and subsequent collapse. An analytical model of expansion joints that takes account of the interaction between adjacent segments of the bridge deck and the effect of impact and restrainers is developed for nonlinear time history analysis. The numerical results show that pounding between adjacent bridge segments could amplify the relative displacement, resulting in the requirement of a longer seat width to support the deck. Pounding results in a transfer of large lateral force from a deck to the other, consequently, results in significant changes in the global response of the participating structural systems. So it is effective to provide a shock absorber between adjacent decks for the mitigation of pounding effect.