A new look at reliability of reinforced concrete columns

This paper presents an investigation on reliability of reinforced concrete columns. For short columns, the fiber model is used for generating failure surfaces and strain and stress histories of both steel and concrete fibers under proportional and sequential loads. Two failure criteria, one based on the collection of peak-load points, the other based on prescribed maximum concrete strains are presented. For slender columns, failure surfaces are generated using a method proposed in 1991 by Ba ant et al. (ACI Structural Journal, 1991, 88, 391–401). The reliability estimation of short and slender columns under random loads is formulated by Monte Carlo simulation in the load space. In this space, isoreliability contours for both deterministic and nondeterministic columns under different load paths and load correlations are plotted. It is demonstrated that these factors may have substantial effects on the reliability of reinforced concrete columns. Therefore, the results of this study can be used to support the consideration of load path and load correlation in the development of improved evaluation and design specifications for reinforced concrete columns.     

Aluminum tubular sections subjected to web crippling—Part II: Proposed design equations

The web crippling design rules in the current American Aluminum Design Manual, Australian/New Zealand Standard, and European code for aluminum structures are assessed. Test strengths of aluminum square and rectangular hollow sections under end-two-flange (ETF) and interior-two-flange (ITF) loading conditions are compared with the design strengths (capacities) obtained using the aforementioned specifications. Furthermore, the test strengths are also compared with the design strengths obtained using the unified web crippling equation as specified in the North American Specification for cold-formed steel structural members. It is shown that the design strengths predicted by the aforementioned specifications are either quite conservative or unconservative, but in general the predictions are unreliable resulting from reliability analysis. Hence, two different unified web crippling equations for aluminum square and rectangular hollow sections under ETF and ITF loading conditions are proposed. The proposed unified design equation (A) uses the same technique as the North American Specification for the unified web crippling equation with new coefficients of C, C_N and C_h determined based on the test results obtained in this study. The proposed unified design equation (B) is similar to the unified web crippling equation in the NAS Specification, and the effect of the ratio N/h is also considered, where N is bearing length and h is the depth of the flat portion of web. Generally, it is shown that the proposed unified web crippling equation (B) compares well with the test results.     

Restructuring retail property markets in Central Europe: impacts on urban space

This paper discusses the changing retail property structures in Central Europe in the aftermath of the integration of these countries in the global economy. In general, within the property market, retail real estate is the market sector that is most affected by internationalization. Therefore, this sector is relatively transparent compared to the office and residential markets. The macro-economic transitions in Central Europe and the integration of these countries in the world economy opened these markets to international retailers. As a result, the retail scene in these countries, combined with the structure of the retail property stock, has changed dramatically. In the late 1990s, Central Europe experienced a retail development boom driven by international hypermarket operators and speculative developers. Shopping centers and hypermarkets became important elements in the urban landscape. However, lack of planning and vision led to chaotic development, and oversupply was the outcome. In the future, public and private actors will need a vision of how the city should develop before embarking on flagship urban projects.

Tests of cold-formed high strength stainless steel compression members

The paper describes a test program on cold-formed high strength stainless steel compression members. The duplex stainless steel having the yield stress and tensile strength up to 750 and 850 MPa, respectively, was investigated. The material properties of the test specimens were obtained from tensile coupon and stub column tests. The test specimens were cold-rolled into square and rectangular hollow sections. The specimens were compressed between fixed ends at different column lengths. The initial overall geometric imperfections of the column specimens were measured. The strength and behaviour of cold-formed high strength stainless steel columns were investigated. The test strengths were compared with the design strengths predicted using the American, Australian/New Zealand and European specifications for cold-formed stainless steel structures. Generally, it is shown that the design strengths predicted by the three specifications are conservative for the cold-formed high strength stainless steel columns. In addition, reliability analysis was performed to evaluate the current design rules.     

An Artificial Neural-network Based Predictive Model for Pre-evacuation Human Response in Domestic Building Fire

The post-1993 WTC attack study (Proulx and Fahy, In: Proceedings of ASIAFLAM’95—An International Conference on Fire Science and Engineering, Hong Kong, 1995, pp 199–210) revealed that occupants took 1–3 h to leave the 110-storey buildings, and the pre-movement reactions could account for over two-thirds of the overall evacuation time. This indicates that a thorough understanding of the pre-evacuation behavioral response of people under fire situations is of prime importance to fire safety design in buildings, especially for complex and ultra high-rise buildings. In view of the stochastic (the positions of the occupants) and fuzzy (uncertainty) nature of human behavior (Fraser-Mitchell, Fire Mater 23:349–355, 1999), conventional linear and polynomial predictive methods may not satisfactorily predict the people’s response. An alternative approach, Adaptive Network based Fuzzy Inference System (ANFIS), is proposed to predict the pre-evacuation behavior of peoples, which is an artificial neural network (ANN) based predictive model and integrates fuzzy logic (if-then rules) and neural network (based on back propagation learning procedures The ANFIS learning architecture can be trained by structured human behavioral data, and different fuzzy human decision rules. The applicability in simulating human behavior in fire is worth exploring.

The activated sludge process—IV: Application of the general kinetic model to anoxic-aerobic digestion of waste activated sludge

This paper discusses the application of the general activated sludge model as set out by Dold et al. (Prog. Wat. Technol.12, 47–77, 1980) and extended by Van Haandel et al. (Wat. Res.15, 1135–1152, 1981), to anoxic-aerobic digestion of waste activated sludge. The laboratory scale experimental investigation comprised a 6 day sludge age activated sludge process, the waste sludge from which was fed to a number of digesters operated as follows: single reactor flow-through digesters at 4 or 10 days sludge age (retention times) under aerobic or anoxic-aerobic conditions (with 1.5 and 4 h cycle times) and 3-in-series flow-through aerobic digesters each with 4 days sludge age; all digesters were fed draw-and-fill wise once per day. The general kinetic model simulated accurately all the experimental data without the need to change the values of the kinetic constants. Both theoretical simulations and experimental data indicate that (i) the rate of volatile solids destruction is not affected by the incorporation of anoxic cycles and (ii) the specific denitrification rate constant in a digester is about two-thirds of that in the secondary anoxic reactor of the single sludge activated sludge system; this allows definition of a fourth denitrification rate constant K₄ for the anoxic-aerobic digester with K₄T = 0.046(1.029)^(T-20) mg(NO₃-N) (mgAVSS d)⁻¹, a constant independent of sludge age. An important consequence of (i) and (ii) above is that the denitrification can be integrated readily into the steady state digester model of Marais and Ekama (Wat. SA2, 163–200, 1976) and used for design purposes.     

Load combination and related fatigue reliability problems

After a general formulation for the load combination problem is sketched, attention is focused on the practical rules to be used in structural design. Three main aspects are found to require further developments:

1. 1. the flexibility of the combination rule to incorporate special situations;

2. 2. the load factor calibration;

3. 3. the understanding of the features the load combination idealization requires when the reliability against a fatigue limit state is studied.

A discussion of these three items forms the core of the paper. Some numerical simulations are also carried out in order to exemplify the fatigue reliability problem.     

A general procedure for first/second-order reliabilitymethod (FORM/SORM)

First/second-order reliability method (FORM/SORM) is considered to be one of the most reliable computational methods for structural reliability. Its accuracy is generally dependent on three parameters, i.e. the curvature radius at the design point, the number of random variables and the first-order reliability index. In the present paper, the ranges of the three parameters for which FORM/SORM is accurate enough are investigated. The results can help us to judge when FORM is accurate enough, when SORM is required and when an accurate method such as the inverse fast Fourier transformation (IFFT) method is required. A general procedure for FORM/SORM is proposed which includes three steps: i.e. point fitting limit state surface, computation of the sum of the principal curvatures K_s and failure probability computation according to the range of K_s. The procedure is demonstrated by several examples.     

How are neighbourhood design features valued across different neighbourhood types?

In this paper, we examine whether implicit prices of neighbourhood design features in the housing market vary significantly across traditional, neo-traditional, and conventional suburban neighbourhood types. The set of neighbourhood design features we examine here include neighbourhood development density, street network connectivity, pedestrian access to transit and commercial stores, and land use mixture. Using data from Washington County, Oregon, we first use statistical procedures to identify distinct neighbourhood types. We then employ hedonic price analyses and a series of spatial Chow tests to obtain implicit prices of design attributes for houses in each neighbourhood type. We find that traditional design features such as higher street network connectivity and better pedestrian access to transit and commercial stores are valued more in the traditional and neo-traditional neighbourhoods, and that conventional neighbourhood features such as lower housing density and higher degree of homogeneous land uses are valued more in the suburban neighbourhoods.

Europäische Baunormen im Test – Charakteristische Werte nach DIN EN 1990, DIN EN 1926 und DIN EN 13162

European Structural Standards under test – characteristic values according to DIN EN 1990, DIN EN 1926 and DIN EN 13162 The determination of nominal value is the starting point for the calculation of the design value. An analysis shows that the required reliability in DIN EN 1990 is not always guaranteed: – application of quantile factors for a confidence level P = 1 – α = 0,50 of assessment via the characteristic value (ENDIN 1990) – use of quantile factors of normal distribution in case of logarithm normal distribution for a confidence level P = 1 – α ≠ 0,50 (ENDIN 1990) – direct assessment of the design value on the basis of a sample size of n = 4, 5, 6, … for a 99,9%‐quantile (EN DIN 1990) – checking whether the underlying distribution and the measure results are in agreement (ENDIN 1926) – estimation of the quantile of the thermal conductivity λ_90/90 from the quantile of the thermal transmission resistance R_10/90 and vice versa (EN DIN 13162). There is a need for consistency between the harmonized European Standards and the technical rules of DIN EN 1990. Therefore, this paper will give recommendations for required corrections.     

Urban Policy in Post-Apartheid South Africa: Context,Evolution and Future Directions

Against a backdrop of definitions and conceptual clarifications of the term urban policy, including its expression in the developing world—and Africa, in particular—this paper reviews the trajectory of urban policy in South Africa post-1994 and comments on future directions and plausible scenarios. In a highly specific context-dependent analysis, the paper argues that, in the first 10 years of democracy, we have seen the creation of democratic, integrated development local government, mass delivery of housing and services, a finely crafted array of capital and operating subsidies for delivery to lowincome households, and a number of programmes intended to enhance the capacity of local government to undertake delivery. All of these have been centrally driven. The counterpoint to the national perspective and frameworks, the paper argues—and in evidence over the past 5 years, in particular—is the increasingly robust role and influence of cities in setting the urban agenda and, in effect, leading urban policy. The paper concludes by examining the many points that contribute to this view.

---

Berlin and Warsaw: in search of a new role in the European urban system

After 1989, the cities of Central and Eastern Europe were engaged in an inter-urban competition, a process characteristic of the urban scene since the beginning of European integration. Being a topic of great interest to researchers, a large body of literature has accumulated on the observed role of capital cities in the region as well as on their potential role in the future. Several researchers have focused on the position as well as the interdependence of Berlin and Warsaw—two urban nodes in what is hypothesized as a future West–East development trajectory (see Domański, 1999). The present paper deals with the emergence and development of metropolitan functions in these two cities. It is based on a comparative research project, which involved a series of structured, in-depth interviews with planners and policy-makers in Germany and Poland conducted by the author during the period 2001–2003. The paper discusses the development factors and their contributions to the metropolitan potential of Berlin and Warsaw. The identification of these factors is a starting point for determining the future position and rank of these two capital cities in the European urban system. The analysis is complemented by a comparison of trends in the employment structure of Berlin and Warsaw during the period 1994–2002. The results allow the author to evaluate some hypotheses posed in strategic planning documents concerning Berlin and Warsaw.

Emergent macrostructures of path-dependent location adoptions processes of firms

Agglomeration of firms in a regional context is a complex process that cannot be tamed easily using traditional economic models. Instead, in this paper, I conducted computer simulations to observe under the assumption of increasing returns how firms choose among competing locations to form regional agglomeration. By designing simple rules of firms’ spatial choice behavior, I observed through such simulations how firms moved across and within regions. The findings showed that firms tended to lock-in a particular region, that is, that region dominated all others in the firms’ movement, reminiscent of market domination of a technology among competing technologies. The emergent macrostructures were surprisingly orderly in that the distributions of sizes of spatial clusters in relation to frequencies followed a logarithmically linear form or a power law. Unpredictability, path dependence, and small events were present in the simulations and can be explained in the context of regional development. Useful insights as to how macrostructures of agglomeration emerge through microbehaviors of firms can be gained through the simulations.

New approach to evaluate the response modification factors for steel moment resisting frames

The design force levels currently specified by most seismic codes are calculated by dividing the base shear for elastic response by the response modification factor (R). This is based on the fact that the structures possess significant reserve strength, redundancy, damping and capacity to dissipate energy. This paper proposed the evaluation methodology and procedure of the response modification factors for steel moment resisting frames. The response modification factors are evaluated by multiplying ductility factor (R _μ) for SDOF systems, MDOF modification factor (R _M ) and strength factor (R _S ) together. The proposed rules were applied to existing steel moment resisting frames. The nonlinear static pushover analysis was performed to estimate the ductility (R _μ), MDOF modification (R _M ) and strength factors (R _S ). The results showed that the response modification factors (R) have different values with various design parameters such as design base shear coefficient (V/W), failure mechanism, framing system and number of stories.     

Urban management in developing countries

This paper reviews current thinking about urban management in developing countries. It does so in the context of recent contributions to a debate on the nature of urban management (Stren, 1993, Cities 10 120–138; Mattingly, 1994, Cities 11(3) 201–205; Werna, 1995, Cities 12(5) 353–359). The paper therefore considers various definitions of the process. This is seen to focus on both the strategic and operational concerns of urban development. It considers the holistic characteristics. This embraces both city and institution building. The contribution of town planning is assessed. This is viewed as a disappointment, despite its potential relevance. The process of providing infrastructure is assessed. This requires all the players to participate, irrespective of organisational location. Integrating the organisational arrangements is therefore acknowledged. This helps to confound attempts to impose an idealised organisational model for urban management, emphasising instead inter-organisational arrangements and their unifying planning process. The wider aim to decentralise urban management is acknowledged. Hence, urban management should be driven by the lowest level of competent government. Urban management is therefore seen to have a twin objective: first, to plan for, provide and maintain a city's infrastructure and services, and second, to make sure that the city's government is in a fit state, organisationally and financially, to ensure that provision and maintenance.     

AN Approach to the Simulation of Coupled Heat and Mass Flows in Buildings

This paper describes the techniques used within the ESP^{R 3} 3 In this context, the term ESP^R refers to the research version of the system as currently under development at various centres throughout Europe including the Universities of Strathclyde and Eindhoven. A separate version of the system is being commercialised by a private company, ABACUS Simulations Limited.
system to represent and solve the heat and mass conservation equations relation to combined building and plant systems. In Particular, it describes the equation-sets used to represent inter-zonal (building) and inter-component (plant) fluid flow and the method used for the integration of the non-linear heat and muss frow equations. By means of a case study, the application in a real design context is demonstrated.     

Web crippling behaviour of laterally restrained cold-formed steel re-entrant profiled deckings

Web crippling failure is often found to be critical in cold-formed steel profiled deckings during construction of composite slabs. Therefore, accurate prediction to the web crippling resistances of profiled deckings over internal supports under hogging moment is highly desirable. This paper presents an extensive experimental investigation into the structural behaviour of laterally restrained re-entrant profiled deckings under concentrated loads. A total of 104 web crippling tests on fully supported re-entrant profiled deckings with nominal yield strengths at 235 and 550 N/mm² are carried out to provide data for direct comparison with design resistances obtained from codified design rules. It should be noted that in the past, little attention has been paid to establish the lateral restraint condition of profiled deckings under concentrated loads in tests. Hence, local section distortion or ‘section spreading’ is often observed in tests but seldom dealt with rigorously during design development. In the present study, effective lateral restraints are provided to the test specimens in order to fully mobilize the web crippling resistances of the profiled deckings. It is found that the measured web crippling resistances are typically 20%–40% higher than those obtained from the codified design rules given in BS5950: Part 6, Eurocode 3: Part 1.3 and the North America Specification, depending on the steel grades and thicknesses, the load bearing lengths as well as the loading conditions.

In general, both BS5950 and Eurocode 3 give conservative web crippling resistances for re-entrant profiled deckings with both low and high strength steel under internal and end loading conditions. Moreover, the corresponding resistance factors determined according to a codified reliability analysis are considerably larger than the required values. Thus, the design rules are reliable and conservative, although they tend to be very conservative for profiled deckings under end loading condition. However, an examination on the design rules given in the NAS shows that only some of them are applicable to predict the web crippling resistances of low and high strength steel re-entrant profiled steel deckings. The design rule for IOF condition always gives both conservative and reliable resistances for both low and high strength steel profiled deckings, compared to the measured values. The design rule for EOF condition is also found to be both conservative and reliable for low strength steel profiled deckings only, but not for high strength steel profiled deckings. The design rules for ITF and ETF conditions are not applicable for both low and high strength steel profiled deckings according to the reliability analyses.

It is demonstrated that a set of new design rules specifically for re-entrant profiled deckings is needed for both improved efficiency and reliability. Moreover, the comprehensive set of test data is readily adopted to calibrate both finite element models and design expressions in subsequent studies.     

How do we understand smart cities? An evolutionary perspective

Smart city approaches in city planning have gained significant momentum in the recent past. While proponents argue that smart cities will bring positive social change by the adoption of ICTs, enriched governance and human capital among the citizenry, opponents point out about the negative effects and gaps exist in their planning and execution. Despite efforts to promote its practice, there has been wide criticism about the concept and the way it has been adopted and implemented. The roles of various players, especially the central role of the private sector, is often challenged in the academic literature. A variety of expectations from various stakeholders make the potential implementation strategies even more complex. The current paper reviews the research in the field to date to find that there are conflicting views in smart city planning, which limit our knowledge about the ‘real’ smart city and its implications for building creative and inclusive urban space. Such uncertainty at the conceptual level, and the heightened importance given by policy makers and markets to its adoption, highlights the need for proper scrutiny. The paper clusters the various views pertaining to the building of smart cities and, thereby, proposes a 3RC framework, consisting of Restrictive, Reflective, Rationalistic and Critical schools, which critically analyses various stages in the development of the field. The overall aim of the paper is to understand how smart cities differ in their meanings, intentions and ‘offerings’.     

The impact of combined sewer overflows on the dissolved oxygen concentration of a river

As described in the preceding paper by Harremoës (Harremoës, Water Res.16, 1093–1098, 1982) it is important to distinguish between removal and degradation of organic matter for non-steady-state discharges to rivers. These effects were investigated to determine the impact of combined sewer overflows on the dissolved oxygen concentration of a small river. Two different effects on the DO-concentration in the receiving river were observed during and after the passage of the bulk of combined sewage discharged at an existing outlet:

1. 1. An immediate effect caused mainly by degradation of the soluble BOD-fraction in the water body and by direct absorption and degradation of organic matter at the bottom.

2. 2. A delayed effect caused by degradation of adsorbed soluble, colloidal and fine particulate organic matter. After the passage of the bulk discharge a delayed effect on the DO-concentration in the river would be observed. This delayed effect lasted 12–24 hours after the discharge event.

Only 4% of the discharged organic matter was degraded during passage of the investigated stretch of the river, approx. 4 km. On the other hand about 35% of the discharged organic matter was removed by transfer to the bottom sediments. The rest was carried past the stretch of river investigated. This results in a rate of adsorption from the water phase of k = 9 m day⁻¹. The deposited organic matter was degraded with a first order reaction rate of K₄ = 0.75 day⁻¹.