On the comparison of the ventilation performance of street canyons of different aspect ratios and Richardson number

In this paper, the ventilation performances of (1) isothermal street canyons of different building-height-to-street-width (aspect) ratios (h/b) and (2) a ground-heated street canyon of h/b=1 at different Richardson numbers (Ri) are examined numerically by solving the Reynolds-averaged Navier-Stokes (RANS) equations with the use of the Renormalization Group (RNG) k-ɛ turbulence model. The mean () and turbulent (ACH’) air exchange rates (ACH) are calculated by the eddy-viscosity model instead of the turbulence kinetic energy (TKE) used elsewhere. For the isothermal street canyons, the ACH’ is found to account for 90% of the total ACH for 0.5 ≤ h/b ≤ 2. Similar to the previous large-eddy simulation (LES) and k-ɛ turbulence model, the magnitudes and shapes of the roof-level profiles of mean and fluctuating vertical winds are close to each other for different h/b. This suggests that turbulent mixing is important for the ventilation of isothermal street canyons. For the ground-heated street canyon, both the mean wind and turbulence are strengthened as illustrated by the increasing and ACH’ with decreasing Ri. A secondary recirculation is developed at the ground-level windward corner that pushes the primary recirculation upward and enhances and ACH as well.     

Effects of multiple parallel fractures on apparent attenuation of stress waves in rock masses

Stress waves propagating through multiple parallel fractures are attenuated (and slowed) due to multiple wave reflections and transmissions at the fractures. This paper presents a theoretical study and the UDEC modeling on the effects of multiple parallel planar fractures on the apparent attenuation of normally incident one-dimensional elastic waves. The case of normal incidence of waves is studied, because we want to remove the influence of the incident angle and to focus purely on the effects of stiffness, spacing and number of parallel fractures.In the theoretical study, an approach is developed to explicitly take into account the attenuative effect of each fracture with the displacement discontinuity model, and to implicitly consider complex interfracture multiple wave reflections with the method of characteristics. The intrinsic attenuation mechanisms are neglected so that the attenuative effects of the multiple reflections can be concentrated on. This approach does not lose the discreteness of wave attenuation at individual fractures, and avoids the difficulty in explicitly determining the complex process of superposition of multiple reflected and transmitted wave fields. With this approach, a set of recurrence equations with respect to particle velocities before and after the fractures are established. These equations are numerically solved with sufficient accuracy. In analysis, there is no restriction to large fracture spacing or to small fracture spacing compared with wavelength. The magnitude of transmission coefficient (T_N) for waves transmitting normally across a set of multiple parallel fractures is calculated as a function of the ratio (ξ) of fracture spacing to wavelength, for different normalized stiffness (k/zω) and for a different number of fractures. Parametric studies are conducted to examine the effects of multiple parallel fractures on wave attenuation, especially in terms of the spacing and the number of fractures. It is shown that the dependence of T_N on the fracture spacing and the fracture number is governed by ξ. In addition, the effects of multiple wave reflections on T_N are quantitatively discussed for different values of ξ.In the numerical modeling, the same problem is studied with a discontinuum-based numerical method, termed as the Discrete Element Method (DEM). The Universal Distinct Element Code (UDEC) is used to model one-dimensional wave propagation in rock masses containing no fractures, a single planar fracture and multiple parallel planar fractures. The modeling results of the transmission coefficient are compared with the theoretical solutions. An agreement between them has been achieved. It is verified that the UDEC is capable of modeling one-dimensional wave propagation across multiple parallel fractures.     

A strategy for the fire testing of reduced scale structural models

A strategy for the fire testing of reduced scale structural models is developed which takes into consideration all significant thermostructural responses. An investigation of the thermal distributions within a structural element allows fire curve, thermal input and structural displacement output to be linked as cause and effect. Dimensional analysis permits the definition of the conditions necessary for dynamic similarity between model and prototype. An equivalent model fire curve is derived which can be mapped by a simple time scale factor on to a standard fire curve, though distortions due to film effects are noted. Errors due to temperature dependent properties are removed due to the nature of model and prototype temperature distributions. The principles are sensibly validated by low temperature experiments on perspex models of different scales. Finally, it is noted that a model test method would be advantageous for the provision of statistically meaningful amounts of indicative test data, with particular reference to parametric investigations. However, it is recognized that one-off full-scale tests must be conducted to provide the best final assessment of fire resistance.Nomenclature d structural element depth or thickness - d _m ;d _p thickness of model and prototype elements - E elastic modulus - F force on a small element slice - h _f film coefficient - k thermal conductivity - L significant longitudinal dimension or span - L _m ;L _p lengths in model and prototype - q heat flux - s scale factor - t generalized time interval - t _m ;t _p model and prototype test time scales - T generalized temperature - T _e equivalent linear temperature distribution - T _f furnace temperature - T _o average temperature through the thickness - T _x curvelinear temperature distribution - T _w element surface temperature - T ₁ –T ₅ thermocouple temperatures through the thickness - u lateral extension - y lateral displacement or bow - coefficient of linear thermal expansion - thermal diffusivity - T temperature difference over the thickness - slenderness ratio - ₁... _n dimensionless groupings - stress in element - _y material yield stress - () _m reference to model test variables - () _p reference to prototype test variables     

ISO 9000 certification and construction project performance: The Malaysian experience

Purpose

This paper explores the relationship between an ISO 9000 certified quality management system (QMS) and elements of performance in construction project environments.

Design/methodology/approach

A survey based approach is used to collect data from project managers working in the Malaysian construction sector in both ISO 9000 certified and non-certified organisations. Three elements of performance are explored: project management (PM) practices, financial management (FM) practices and Project Success. The Project Management Performance Assessment model (PMPA) (Bryde, 2003) is used as the framework for assessing PM Practices. 336 completed questionnaires are analysed, with a group of 73 being from ISO 9000 certified companies (a response rate of 48.3%) and a group of 262 being from non-certified companies (response rate = 32.6%). MANOVA are used to explore differences in levels of performance between the two groups.

Findings

Overall there is significance difference in mean scores at the 5% level in respect of each of the PM and FM Practice elements of performance, indicating that ISO 9000 certified companies have enhanced levels of performance in their project environments compared to those in non-certified companies. The two exceptions are the PM Practice related to establishing partnerships and managing resources and the FM Practice related to allowing for inflation and price escalations. The results also indicate that ISO 9000 certification has a positive moderating effect on the casual relationship between PM Practices and Project Success. Based on the survey results a Project Management Performance Assessment for Construction (PMPAC) model is developed, which extends the PMPA to include performance enablers linked to financial management activities.

Research limitations/implications

The survey focuses on the construction sector in Malaysia and further work is required to see if the findings are applicable to other countries and also to other business sectors beyond the construction sector.

Originality/value

The research reported in this paper is original in that prior research into the link of ISO 9000 certification and dimensions of organizational performance has not explicitly focused on project environments. The research findings provide evidence that those seeking to enhance their project performance could gain benefits from developing a QMS and seeking ISO 9000 accreditation. However the finding also indicate that an approach to performance management based solely on establishing a certified QMS may have its limitations in terms of establishing processes for managing the relationships on a project through partnership approaches and in dealing with uncertainty in the external environment, such as price fluctuations. The PMPAC model presented in this paper provides a framework for those working in construction project environments to ensure their project management systems incorporate the key activities that enable better performance.     

Effects of boundary conditions on the energy absorption of thin-walled polymer composite tubes under axial crushing

Polymer composite tubes can be designed to absorb high levels of impact energy by progressive crushing. When a tube is crushed onto a flat platen, energy is absorbed by bending failure of the plies, delamination and friction mechanisms. In the present work, significant increases in energy absorption are shown when a shear mode of failure is initiated by crushing the tube onto a radiused plug (or initiator). A study of plug radius, R, normalised with respect to the tube wall thickness, t, in the range of 0R/t5 for circular tube diameter/thickness ratios of 10<D/t<33 was undertaken with continuous filament random mat glass/polyester composite. Different radii plugs lead to significantly different deformed shapes and crush zone morphologies. Large radius initiators (R/t>2) cause the tubes to split and energy is absorbed primarily through friction and axial splitting. As the initiator radius decreases, the amount of through-thickness shear damage in the fronds increases along with specific energy absorption (SEA). When the plug radius becomes small compared to the wall thickness (R/t<0.75) a debris wedge forms between the initiator and the tube and acts like a larger radius initiator. The highest energy absorption was seen to occur at R/t1 when through-thickness shear damage was induced. In this range, under static loading conditions, SEA was seen to be higher than that for tubes crushed onto a flat platen.     

Measurements of the characteristic lengths of smoke detectors

The dynamic performance of point-type smoke detectors is described by a simple model including two independent parameters, the static response threshold, and the characteristic length of the detector. An experimental system with constant rate of increase of smoke density under varying velocity conditions is used to determine the model parameters.Nomenclature k constant smoke density gradient (dB/m/s) - L characteristic length of the detector (m) - m _i smoke density inside the detector (dB/m) - m _o smoke density outside the detector (dB/m) - m _or measured smoke density at response (dB/m) - m _r response threshold of the detector (dB/m) - t time(s) - v gas flow velocity at the detector (m/s) - time constant(s)     

Fire protection of flammable work stations in the clean room environment of a microelectronic fabrication facility

An applied engineering program is described which investigates the fire safety of combustible wet stations used within microelectronic clean room fabrication facilities. The main concern involves the impact of a wet bench fire on the clean room environment of the fabrication facility. The effectiveness of the installed fire detection and suppression systems are discussed as well as the additional steps which should be taken in order to insure early detection and suppression of fires within wet benches. Reference: Fred L. Fisher, Robert Brady Williamson, Gary L. Toms and Dennis M. Crinnion, Fire Protection of Flammable Work Stations in the Clean Room Environment of a Microelectronic Fabrication Facility,Fire Technology, Vol. 22, No. 2, May 1986, p. 148.     

A smoke-filling simulation model and its engineering applications

A brief presentation of the computer model DSLAY1, which describes the smoke-filling process in a single enclosure, is first given in this paper. Also some computed data of the model are compared with experimental results to show the agreement between theory and experiment. In the latter part of the paper computed results are presented for areas where the model has been used for different fire engineering applications. The main purpose is to show that zone models like DSLAY1 are useful tools to predict the heat and smoke conditions in single enclosures as a result of growing fires. DSLAY1 is an interactive computer program. The user converses with the program via a terminal connected to the computer. The dialogue is governed by commands adapted to the concepts of the user. Reference: Staffan Bengtson and Bengt Hägglund, A Smoke-Filling Simulation Model and Its Engineering Applications,Fire Technology, Vol. 22, No. 2, May 1986, p. 92.     

Start-up activities,individual characteristics,and the regional milieu: Lessons for entrepreneurship support policies from German micro data

This paper contributes to empirical research on the role of regional policy for entrepreneurship by focusing on the link between two stylized facts that emerged from a number of studies for Germany and other countries: Entry rates differ between regions, and the propensity to become an entrepreneur is influenced by socio-demographic variables and attitudes. We develop a theoretical framework to discuss this link, and we test whether for a person of a given age, degree of schooling, attitude towards risk etc. regional variables and, therefore, regional policies, do matter for the decision to start a new business ceteris paribus. Our econometric study is based on data for 10.000 persons from a recent representative survey of the population in ten German planning regions, the Regional Entrepreneurship Monitor (REM). We use a version of the probit model that takes care of the regional stratification of the data, and the results of the nonlinear models are carefully interpreted and illustrated. We find that the propensity to step into self-employment is, among others, higher for males, unemployed, people with contacts to a role model, and with past entrepreneurial experience, who live in more densely populated and faster growing regions with higher rates of new firm formation, while risk aversion and high prices of land have the opposite impact. Interestingly, it does not matter whether the region has a left or right government. However, many implications for entrepreneurship supporting policies in German regions are discussed in the final section.Research for this paper was done as part of the project Regional Entrepreneurship Monitor REM Germany financially supported by the German Research Foundation (DFG STE 628/7-1/2 and WA 610/2-1/2). We thank two anonymous referees and the guest editors of this issue for comments that led to an extensive revision of an earlier version.     

Support provided to rock excavations by a system of two liners

The support provided by a system of two liners to a cylindrical excavation which is subjected to a shear stress at infinity is considered. The tensile, shear and normal stresses and the rotation of a material element at the surface of the excavation before and after the liners are applied are calculated to second order in the thickness parameter using the theory of plane strain in elasticity. Stress is transferred from the rock mass to the liners. To first order in the thickness parameter the changes in the stresses and the rotation do not depend on the order in which the liners are bonded to the surface of the excavation. A small dependence on the order in which the liners are attached was found at second order in . Effective boundary conditions on the shear and normal stress at the surface of the excavation which could replace the liner system were obtained.     

An empirical estimation of regional production functions for the U.S. manufacturing industry

Five different production functions for 50 states and the District of Columbia in the U.S. are estimated and compared based on the 1987 data from the Census of Manufacturers. The Cobb-Douglas function can be rejected. The CES yields a negative value of the elasticity of substitution (). In the translog function, the coefficient of logK _t has a wrong sign and is insignificant. The coefficient ofK _t ^0.5 L _t ^0.5 in the generalized Leontief function is insignificant at the 5% level. It appears that the new CES function (Bairam, 1989, 1991) yields the best statistical results: is estimated to be 1.56, and total output elasticity ranges from 0.85 to 1.12, which can partly be explained by different values of theK/L ratio.Insightful comments from two anonymous referees are appreciated.     

Thirty years with spatial and intertemporal economics

In this paper the practical origin and development of the spatial and intertemporal price equilibrium (SIPE) models are chronologically followed around the personal life of the author. The fact that both the Marshallian (quantity) formulation and the Walrasian (price) formulation have been with the Takayama-Judge models in the primal-dual (purified-duality) relationship from the outset is pointed out. Historical use and abuse of large scale models in the past two decades, closely related to the SIPE models, are discussed. The author acknowledges recent developments of methodologies by younger generation researchers in this field and concludes that along with the recent development of high-powered computers and softwares, there will be a number of interesting and relevant SIPE model applications in the near future.This paper was first read at an international conference on Trade, Knowledge and the Network Economy, in Mallacoota, Victoria, Australia, and was revised to present for the workshop entitled Advances in Spatial Equilibrium Modeling held at the new Tinbergen Institute in Amsterdam, Netherlands on January 24–25, 1994.The author would like to express his gratitude to Professors Martin Beckmann, Peter Nijkamp, Dr. John R. Roy and an anonymous referee for their numerous comments and advice in revising this paper. Any remaining omissions and commissions are my own.This paper was presented in draft form at an International Workshop on Trade, Knowledge and the Network Economy, held in December 1992 in Mallacoota, Australia.     

Optimum stiffened panel design with fundamental frequency constraint

A generic analysis/design method for prismatic plate assemblies, using exact plate stiffnesses which are transcendental functions of loading and/or vibration frequency, has long been validated by the established program . Hitherto vibrations were permitted only in analysis because design uses the Wittrick–Williams algorithm to modify the design predicted by a linear optimiser to be ‘just stable’ by scaling all layer thicknesses by F. This works because buckling loads, unlike the fundamental frequency f₁, vary monotonically with F. The paper considers additionally scaling all plate breadths by F^α such that the buckling loads and f₁ all vary monotonically with F. Theoretical consideration of simple limiting cases establishes bounds on the permitted values of α as 0.1≤α≤0.4. Then results for typical stiffened panels demonstrate the method to be correct and are used to investigate the value of α which is most effective in returning stabilised designs of least mass and with least computation.     

Postflashover fires — an overview of the research at the national research council of Canada (NRCC), 1970–1985

The NRCC model of fully developed compartment fires is discussed. Although the mathematics involved is quite simple, it allows a rather comprehensive simulation of the fire process. The model offers an explanation for the findings that ventilation control is related to the pyrolysis mechanism and is not a result of scarcity of air in the fire compartment, and that thermal feedback is of secondary importance in the burning (pyrolysis) of cellulosic fuels. Another feature of the model is the introduction of the normalized heat load concept. The normalized heat load is a scalar quantity that depends on the total heat absorbed by the compartment boundaries during the fire incident, and is practically independent of the temperature history of the fire. A simple explicit formula has been proposed and proved experimentally to describe the normalized heat load for real-world fires with fair accuracy. The normalized heat load concept offers a simple means for converting fire severities into fire resistance requirements, and makes it possible to design buildings for prescribed levels of structural fire safety. The potential of fires to spread by convection and the expected characteristics of fires of noncharring plastics are also discussed. Reference: T. Z. Harmathy, Postflashover Fires—An Overview of the Research at the National Research Council of Canada (NRCC), 1970–1985,Fire Technology, Vol. 22, No. 3, August 1986, p. 210.     

Deviation of hydraulic fractures through poroelastic stress changes induced by fluid injection and pumping

This paper presents an analysis of the deviation of hydraulic fractures associated with the poroelastic change of the in situ stress field caused by fluid injection and pumping in the reservoir. This mechanism is studied within the confines of a simple model involving one injection and one pumping well, and a hydraulic fracture propagating along the path initially equidistant from the two wells. Analysis of the fracture deviation from its straight-ahead path and determination of the conditions leading to attraction of the fracture by the injection well are both based on a theoretical study of the stress trajectories. Comparison of the analytical prediction of the fracture path with the computed path using a numerical technique shows excellent agreement between the two methods, provided that a certain dimensionless toughness is small.The principal results of this study can be summarized as follows. First, a fracture propagating along a path, initially midway between an injection and a pumping well, will always be deviated by the injection well due to the shear stress induced by fluid injection and pumping along the initial path.Second, the injection well acts as an attractor of hydraulic fractures propagating within its “attraction basin”. Then, the fracture will propagate toward the injection well rather than simply be deviated by it. One of the features of this attraction basin is the existence of a “fracture barrier” characterized by a 90° rotation of the principal stress directions, with respect to far-field principal directions.Third, fracture deviation and attraction towards the injection well appears to be primarily controlled by only two dimensionless quantities: ., the ratio of the stress deviator at infinity over the characteristic stress σ∗ associated with injection and pumping of fluid, and π = 4ct/L², a dimensionless time (where c is the diffusivity and L is the half-distance between the two wells). The number of significant parameters is thus remarkably less than expected from a dimensional consideration. Only in the region close to the injection well is there an influence of an additional number , the ratio of the difference between the mean pressure at infinity and initial pore pressure to the characteristic stress σ∗.     

Bridge afflux analysis through arched bridge constrictions using artificial intelligence methods

Although many studies have been carried out for estimating the afflux through modern straight deck bridge constrictions, little attention has been given to medieval arched bridge constrictions. Hydraulic Research Wallingford in the UK (Brown, P.M., 1988 Brown, P. M. 1988. Afflux at arch bridges, Wallingford, , UK: HR Wallingford. Report SR 182 [Google Scholar]. Afflux at arch bridges. Report SR 182. Wallingford, UK: HR Wallingford) recently published a major coverage of both experimental and field afflux data obtained from arched bridge constrictions. The report pointed out that the present day formulas developed for estimating the bridge afflux are inadequate to apply to ancient arched structures. Therefore, this study aimed at developing new afflux methods for arched bridge constrictions using multi-layer perceptrons (MLP) neural networks, radial basis function-based neural networks (RBNN), generalised regression neural networks (GRNN) and adaptive neuro-fuzzy inference system (ANFIS) model. Multiple linear and multiple nonlinear regression analyses were also used for comparison purposes. Mean square errors, mean absolute errors, mean absolute relative errors, average of individual ratios between predicted and actual values, and determination coefficients were used as comparison criteria for the evaluation of model performances. The test results showed that MLP, RBNN, GRNN, and ANFIS models gave reasonable accuracy when applied to both the field and experimental data collected by Hydraulic Research Wallingford.     

New developments in the Integrated Stress Determination Method and their application to rock stress data at the Äspö HRL, Sweden

The Integrated Stress Determination Method (ISDM) is a powerful tool for estimating the regional stress tensor from in-situ measurements of local stress tensors using a wide variety of stress measuring techniques. This study presents new developments of the ISDM: The stress field may be described with up to 12 model parameters; and is applicable to data from CSIR- and CSIRO HI-type of overcoring devices, hydraulic fracturing, hydraulic tests of pre-existing fractures (HTPF), as well as to combined data sets. Furthermore, in combined data sets, the hydraulic fracturing and/or HTPF data may be used to constrain the average elastic parameters, Young's modulus and Poisson's ratio.The new ISDM developments were applied to the extensive and recently re-analysed rock stress data at the Äspö Hard Rock Laboratory. The results reveal a good fit of the re-analysed data. Overall, the re-analysis indicates that the stress field at Äspö HRL is relatively well constrained and consistent with depth. The NE-2 Fracture Zone influences the stresses, and dividing the regional stress field into a NW and a SE stress domain. When the hydraulic fracturing data were used to constrain the average elastic parameters, Young's modulus, E, and Poisson's ratio, ν, quite similar results were obtained ( and ν=0.33) compared with results from biaxial tests of overcore samples ( and ν=0.26).     

Directions for improving manual fire suppression using a physically based computer simulation

The Swedish Fire Research Board and the U.S. Federal Emergency Management Agency are sponsoring a project to further the understanding of the basic mechanisms involved, as well as to support the development of standards for and to seek ways of improving the performance of portable fire suppression systems used by fire departments.This paper describes a physically based computer model developed to simulate one aspect of the problem: the manual suppression of postflashover fires. This includes: (1) an overview of the physical basis behind the model; (2) a comparison of model predictions with available experimental data, and (3) an analysis of fire suppression effectiveness using the model.The analysis concludes that, when direct access and extinguishment of the burning fuel is not possible, improved fire control occurs with water sprays having a Rosin-Rammler distribution of droplet sizes with volume-median-drop diameters in the 0.15 to 0.35 mm range. This agrees with available experimental data. It is also shown that fire fighting venting and standoff distance requirements may lead to more severe fires requiring more water for control; although venting and water spray induced air/gas flow also serve to channel hot steam and gases away from the fire fighter adding to his safety. The analysis also shows that allowing higher gas and surface temperatures at fire control through improved fire fighter protective clothing and equipment design reduces water flow rate requirements. Additional experimental work is recommended before all these conclusions are considered definitive. Reference: L. M. Pietrzak and G. A. Johanson, Directions for Improving Manual Fire Suppression Using a Physically Based Computer Simulation,Fire Technology, Vol. 22, No. 3, August, 1986, p. 184.     

Optimisation of the design of infrastructure components subject to progressive deterioration and extreme loads

The construction of new infrastructure requires solutions that maximise the benefit while meeting acceptable safety levels. The solution to this problem can be obtained through a structural cost-based optimisation. This paper integrates a life-cycle cost optimisation model developed by Rackwitz (2000 Rackwitz, R. 2000. Optimization – the basis for code making and reliability verification. Structural Safety, 22: 27–60. [Crossref], [Web of Science ®] , [Google Scholar]) with a structural deterioration model that combines the action of progressive degradation (e.g. corrosion, fatigue) and sudden events (e.g. earthquakes). The structural condition at a given time is measured in terms of the system's remaining life, which can be measured in practice through any structural performance indicator (e.g. ductility). It is assumed that sudden events conform to a compound point process with shock sizes and interarrival times that are independent and identically distributed random variables. Deterministic and random progressive deterioration models are also included in the formulation. Randomness in progressive deterioration is modelled as a point process with known arrival times and random shock sizes. Structural reliability is evaluated against prescribed design and operation thresholds that can be used to establish limit states or intervention policies. The entire model is illustrated with an example that compares several life-cycle models showing the importance of taking into account the damage history in evaluating the performance of infrastructure systems.