Study of the Ultimate Load Capacity of K-Type Tube-Gusset Plate Connections

In order to investigate the ultimate load capacity of K-type tube-gusset plate connections with stiffened plate, the static tests of five full-scale specimens were conducted in this study. The results indicate that the end stiffened plate is critical for improving the load capacity of the connections. In addition, the parametric nonlinear finite element analysis of the K-type tube-gusset plate specimens was performed with account of such non-dimensional parameters as chord diameter-to-thickness ratio (γ), plate width-to-chord diameter ratio (α), plate thickness-to-chord thickness ratio (\(\tau_{1}\)), stiffened plate thickness (t_d), and nominal-to-yield stress ratio (η). The above analysis implies that the ultimate load capacity decreases with the increment of γ and increases with the increment of α and \(\tau_{1}\), while it is only slightly affected by the stiffened plate thickness. Compare the results of the finite element analysis with assessment by design guides existing. Based on the former results, an equation for estimating the load capacity of K-type tube-stiffened gusset plate is proposed.     

Behavior of thin-walled circular hollow section stub columns under axial compression

Thin-walled steel circular hollow section (CHS) is widely used in wind turbine towers, where the tube is subjected to axial load combined with bending moment. Understanding the behavior of axially loaded thin-walled tubes with large diameter-to-thickness (D/t) ratios is crucial for the design of such structures. To investigate the behavior of axially loaded thin-walled circular hollow section steel tubes, 16 stub columns were tested with the D/t ratio ranging from 75 to 300. The experimental results showed that the compressive strength decreased sharply with the increase of the D/t ratio. The experimental result indicated that the tubes with smaller D/t ratios failed with outward deformation without visible local buckling. With the increase of the D/t ratio, local buckling appeared at the peak load. The finite element method was used to model the behavior of axially loaded stub columns. The experimental results were used to validate the accuracy of the finite element results. Based on the finite element model, the influences of the D/t ratio, the initial geometric deformation and the initial residual stress were analyzed. Design guidelines in Eurocode3, AISC-LRFD, AS4100 and S16-9 on thin-walled steel members were used to compare with the experimental and calculated results. Among them, the results based on AS4100 were the closest to the experimental results.     

Improving predictions of heat transfer in indoor environments with eddy viscosity turbulence models

Heat transfer modelling in indoor environments requires an accurate prediction of the convective heat transfer phenomenon. Because of the lower computational cost and numerical stability, eddy viscosity turbulence models are often used. These models allow modification to turbulent Prandtl number, and near wall correction which influences stagnation points, entrainment, and velocity and time scales. A modified v ²–f model was made to correct the entrainment behaviour in the near wall and at the stagnation point. This new model was evaluated on six cases involving free and forced convection and room airflow scenarios and compared with the standard k–ε, and k–ω–SST models. The results showed that the modification to the v ²–f model provided better predictions of the buoyant heat transfer flows while the standard k–ε failed to reproduce and underestimate the convective heat transfer. The k–ω–SST model was able to predict the flow field well only for a 2D square cavity room, and 3D partitioned room case, while it was poor for the other four cases.     

Effects of inner sleeves on the inner frictional resistance of open-ended piles driven into sand

In open-ended piles, inner friction is developed between inner pile shaft and the inner soil. Inner frictional resistance depends largely on the degree of soil plugging, which is influenced by many factors including pile diameter, relative density and end conditions of piles. In this paper, effects of inner sleeves on inner frictional resistance are discussed. The experiments were conducted on a medium-dense sandy ground using laboratory-scale piles. It was observed that the piles penetrated under partially-plugged or unplugged state. The results suggest that inner frictional resistance, Q_in increases with sleeve height, l linearly and requires 2D (D is pile outer diameter) of l to produce a large as 50% of Q_t by Q_in (Q_t is total resistance). The results also indicate that bearing capacity increases with wall thickness at the pile tip, which can be attributed to the increase in annular area. The results also indicate that soil plug height is independent of sleeve height. The results also reveal that the penetration of straight piles is closer to unplugged state than the sleeved piles. The results of incremental filling ratio and plug length ratio also indicate that the degree of soil plugging is affected by the sleeve height.     

Cardiff theory: Web panel aspect ratio limits and their relation with inclination angle of membrane tensile yield strength

Theoretical predictions of the ultimate shear resistance of slender-plate girders are broadly based on either Cardiff theory or Höglund’s theory. Cardiff theory assumes an equilibrium stress field (tension field) in the girder, which satisfies the theoretical conditions for a lower-bound strength prediction, provided the material possesses sufficient ductility for the stress field to be developed. Previous investigators did not determine the limits of web panel aspect ratio (b/d) or its relation to inclination angle of membrane tensile yielding strength (IAMTYS), which are important parameters in Cardiff theory. This paper presents a theoretical analysis to identify the limits of b/d that can be applied to Cardiff theory and their relation with c/b, the ratio of the distance where the plastic hinges form in the flanges (c) to the panel width (b). This analysis is based on previously published experimental results of ninety six steel plate girders subjected to shear. We make recommendations regarding (1) the optimum limits of panel aspect ratio for a given IAMTYS, and (2) the range of c/b values that can be used to predict the ultimate shear resistance using Cardiff theory.     

The internal force relationship of rectangular and I-section for bi-linear hardening material with limit strain

Based on bilinear stress-strain constitutive law σ = f (ε), the elastic to fully plastic analysis of bending of rectangular-section and bi-symmetrical I-section beams with the influence of axial load is presented for hardening material with limit strain. The variation of the applied bending moment with the axial force for the fully elastic, elastic-plastic, and fully plastic conditions is given in analytical form. The Internal force relationship of the elastic limit is the same for both hardening and non-hardening material and independent of the geometry of the beam section. However, for the elastic-plastic and plastic limits, the relationships are dependent of the hardening parameter β _q, limit strain ε _lim and the geometry of the beam section for neutral axis (N.A) inside the cross section. When N.A outside the cross section, the relationships are dependent of hardening parameter β _q and limit strain ε _lim but independent of the geometry of the beam section. The results given by the analytical expressions reduce to the ones for non-hardening material are in good agreement with the existing results.     

Utilizing the strength conversion factor in the estimation of uniaxial compressive strength from the point load index

The strength conversion factor (k) is the ratio between the uniaxial compressive strength (UCS) and the point load index (PLI). It has been used to estimate the UCS from the PLI since the 1960s. Many researchers have investigated the relationship between UCS and PLI for various rock types of different geological origins, such as igneous, sedimentary, and metamorphic rocks. In this study, the k values for subclasses of igneous (pyroclastic, volcanic, and plutonic), sedimentary (chemical and clastic), and metamorphic (foliated and nonfoliated) rocks were evaluated. For this purpose, UCS and PLI data for a total of 410 rock samples extracted from literature published around the world as well as UCS and PLI data obtained in this work for 80 rock samples taken from the Eastern Black Sea Region in Turkey were evaluated together to determine the k values of different rock classes. Strength conversion factors were obtained using zero-intercept regression analysis, formulation, and a graphical approach. This study confirmed that there is no single k value that is applicable to all rock classes. According to statistical analyses, k varied between 12.98 and 18.55 for the rocks studied. These findings demonstrate that the k values derived in this work can be reliably used to estimate the strengths of rock samples with specific lithologies.     

Effects of geometry on the sound field in atria

The atria in commercial buildings are widespread. However, the sound environment has not been given sufficient consideration. Geometry affects the acoustics in the atria. The concept of geometry in this paper includes five parameters, namely, length (l), height (h), aspect ratio of length to width (l/w), skylight form and slope, to provide suggestions for the acoustic environment design in atria. A series of computer models are simulated to analyse the effects of the form parameters on the acoustic environment, such as sound pressure level (SPL) and reverberation time (T₃₀ in this paper). The results indicate that with an increase in the length or height, the values of the average SPL decrease, and the trends of the curves are logarithmic. For an increasing length, the T₃₀ increases first sharply and then slowly. With the scattering increasing, the increment of the T₃₀ is smaller. For an increasing height, the changes of T₃₀ are determined by the absorption and scattering. In terms of the aspect ratio of l/w increasing for a given volume and area, the average SPL values approximately decrease linearly; furthermore, the T₃₀ decreases unless the atrium is extremely high. The T₃₀ is the longest for a flat skylight compared to that of other forms, and it is shorter when the skylight has a slope, including either a single or a double-pitch skylight. It can decrease nearly by 40% when the angle of the lean-to skylight is 7°. The T₃₀ is lower and the amount of decrease is considerably smaller for an increasing slope. When the absorption is evenly distributed in the atria, the skylight has minimal effect on the average SPL or T₃₀ values. Additionally, the classical formula can approximately calculate the SPL distribution unless the atrium is in a form of long space. The Arau-Purchades formula is generally appropriate to predict T₃₀ with uneven absorption distributions unless the absorption or scattering coefficient is low.     

Investigation of correlations between shear wave velocities and CPT data: a case study at Eskisehir in Turkey

Seismic waves result from fault movement during earthquakes. Depending on the features of the physical environment through which they pass, there are variations in the velocity and amplitude of body waves, which occur underground, and surface waves, which occur on the Earth’s surface. The ratio of shear wave velocity (V _s) to near-surface velocity is a parameter used widely in land use planning to predict the potential for amplified seismic shaking, especially in urban areas. The main objective of this study was to estimate V _s by using cone resistance (q _c) and lateral friction (f _s) for a study area at Eskisehir Graben, to help mitigate geotechnical earthquake engineering problems in civil engineering and land use planning. In geotechnical shallow soil research, certain geophysical methods are used for measuring V _s —a major form of seismic energy propagation—at the near surface. In this study, cone penetrometer data collected from seismic cone penetration tests (SCPT) includes q _c, f _s, and downhole V _s. S-type seismic energy waveforms, which are produced on the surface, were measured at different depths using an S-type geophone in the city center of Eskisehir via SCPT. With SCPT, q _c, friction ratios (R _f), and V _s values were measured at 42 different test points. R _f properties are associated with soil thickness, and these were compared with dynamic soil properties (V _s) using a standard statistical method; we calculated correlations amongst V _s, q _c, and R _f measured from cone penetration tests.     

Construction and verification of a unified <Emphasis Type="Italic">p</Emphasis>–<Emphasis Type="Italic">y</Emphasis> curve for laterally loaded piles

Estimation of the lateral pile load capacity is the key design procedure for structures where lateral loads are predominant, such as bridges, tall buildings and offshore platforms. In the process of laterally loaded pile design, the p–y curve method is the mainstream method and preferred by designers compared to the elastic continuum or finite element analysis. The traditional p–y curves are derived from some specific field tests and limited data, which do not reflect the overall conditions. In this study, a unified p–y curve based on the stress increment perspective was constructed by introducing Vesic cavity expansion theory and considering the actual stress state of the surrounding soils. The proposed p–y curve combines the contributions of the expansion-induced soil radial stress increment, vertical stress increment and lateral soil resistance caused by deep pile rotation. To validate the proposed method, case examples of lateral pile load tests in various soil conditions were prepared and used to compare the p–y curves from the test results and proposed methods. The p–y curves calculated from the proposed method show reasonable agreement with measured results and give a good prediction in large deformation analysis.     

A Method to Assess the Accuracy of Pseudo-Random Number Sampling Methods from Evacuation Datasets

We propose a method for assessing the accuracy of pseudo-random number sampling methods for evacuation modelling purposes. It consists of a systematic comparison between experimental and generated distributions. The calculated weighted relative error (E _{w_rel} ) is based on the statistical parameters as central moments (mean, standard deviation, skewness and kurtosis) to shape the distribution. The case study involves the Box–Muller transform, the Kernel-Epanechnikov, the Kernel-Gaussian and the Piecewise linear generating samples from eight evacuation datasets fitted against normal, lognormal and uniform distributions. Keeping in mind that the Bos Muller method has two potential sources of error (i.e. distribution fitting and sampling), this method produces plausible results when generating samples from the three types of distributions (E _{w_rel}  < 0.30 for normal, lognormal and uniform distributions). We also fund that the Kernel Gaussian and the Kernel Epanechnikov methods are well accurate in generating samples from normal distributions (E _{w_rel}  < 0.1) but potentially inaccurate when generating samples from uniform and lognormal distributions (E _{w_rel}  > 0.80). Results suggest that the Piecewise linear is the most accurate method (E _{w_rel}  = 0.01 normal; E _{w_rel}  = 0.04 lognormal; E _{w_rel}  = 0.009 uniform). This method has the advantage of sampling directly from empirical datasets i.e. no previous distribution fitting is needed. While the proposed method is used here for evacuation modelling, it can be extended to other fire safety engineering applications.     

Buckling of fixed-ended concrete-filled steel columns under axial compression

In recent years, due to a relatively high price increase of nickel alloys, there is an increase in demand for lean duplex stainless steel (LDSS) with a low nickel content of ~1.5%, such as grade EN 1.4162. LDSS offers roughly twice the strength compared to austenitic stainless steels and has great potential for expanding future structural possibilities, enabling a reduction in the section sizes leading to lighter structures. This paper reports the buckling behavior of fixed-ended concrete-filled LDSS tubular (CFDSST) columns with L-, T-, and +-shape (Non-Rectangular Sections or NRSs) sections and a representative square section with varying lengths through Finite Element (FE) analysis. The purpose is to compare and assess the strength and deformation characteristics as well as the failure modes of such columns. It is seen that concrete-filled tubular columns with NRSs offered a better performance for all lengths considered, especially the T-shaped and +-shaped sections, in terms of strength. The influence of the cross-sectional shapes on the ε _u becomes less significant with increasing λ, but becomes increasingly significant with decreasing λ. The design standards show over conservative results for square and L-shape sections and conservative for T-shape and +-shape sections.     

Dynamic sub-grid scale turbulent Schmidt number approach in large eddy simulation of dispersion around an isolated cubical building

In this paper, the effects of the sub-grid scale (SGS) turbulent Schmidt number, Sc _SGS, on the large eddy simulation of dispersion on and around an isolated cubical model building with a flush vent located on its roof are examined. Constant and dynamic Sc _SGS approaches for SGS turbulent mass flux modeling are employed. Simulation results are compared with the available wind tunnel measurements. Furthermore, the influence of the grid resolution on the accuracy of results predicted by the dynamic Sc _SGS approach is investigated. Detailed statistical analysis of Sc _SGS demonstrates that the dynamically computed Sc _SGS at different locations varies by a factor of almost 5 and a considerable deviation of Sc _SGS from its common values of 0.5 and 0.7 occurs. Particularly, in the vicinity of the building where the concentration gradients are noticeable, Sc _SGS has a larger variation. Also, the probability of occurrence of 0.2 < Sc _SGS <1.5 is more than 90 percent and the Sc _SGS mean values are nearly around 0.8 to 1 with a maximum variance of 0.2. In addition, by refining the grid, the differences between the predictions of constant and dynamic Sc _SGS approaches decrease. This is due to the reduction of sub-grid scales contribution to turbulent dispersion. It is confirmed that dynamic Sc _SGS approach is a practical alternative to the constant Sc _SGS approach, effectively eliminating a user-defined model coefficient.     

Ultimate capacity prediction of axially loaded CFST short columns

Composite columns have superior strength and ductility performance, and they have become more widely accepted in the engineering applications. However, the filled tubular columns require more attention. This study aims to present a new formulation for the axial load carrying capacity (N _u ) of circular concrete filled steel tubular (CFST) short columns having various geometrical and material properties. Although there have been some empirical relations for predicting N _u in the literature, genetic algorithm based explicit formulation is not available. In the current study, 314 comprehensive experimental data samples presented in the previous studies were examined to prepare a data set for training and testing of the prediction model. The prediction parameters were selected as outer diameter of column (D), wall thickness (t), length of column (L), compressive strength of concrete (f _c ), and yield strength of steel (f _y ). The prediction model was obtained by means of gene expression programming (GEP). The proposed model was compared with available ones presented in the current design codes (ACI, Australian Standards, AISC, AIJ, Eurocode 4, DL/T, and CISC) and some existing empirical models proposed by researchers. The prediction performance of all models were also evaluated by the statistical parameters. The results indicated that the GEP model was much better than the available formulae, yielding higher correlation coefficient and lower error.     

Occupants’ interactions with windows in 8 residential apartments in Beijing and Nanjing,China

Occupants’ interactions with windows influence both building energy consumption and exposure to airborne pollutants indoors. Occupants’ window opening behavior varies from region to region due to physical environmental factors and social reasons. China is now confronting severe atmospheric pollution, which may affect occupants’ window opening behaviors. A field study was conducted in 8 naturally ventilated residential apartments in Beijing and Nanjing, China. This involved periodically monitoring window states of eight residential apartments within each season from October 2013 to December 2014 by magnetic induction devices (TJHY, CKJM-1). Relationships between the probability of window opening (p) and explanatory variables, including outdoor air temperature (t _o), outdoor relative humidity (RH), outdoor wind speed (V _s), and ambient PM2.5 (particles with aerodynamic diameter less than 2.5 microns) concentrations (C _p), were analyzed. Stochastic models of occupants’ interactions with windows in monitored residences were established via univariate and multivariate linear logistic regression for both cities. According to the results, t _o is the most important explanatory variable affecting occupants’ interactions with windows in monitored residences. The best multivariate linear logistic model result from the “backward selection” procedure based on “Akaike Information Criterion” (AIC) includes t _o, RH, V _s and C _p as explanatory variables, which implied that outdoor air quality, represented by C _p, has become a concern affecting Chinese residents’ interactions with windows.     

Effect of Elevated Temperatures on Mechanical Performance of Normal and Lightweight Concretes Reinforced with Carbon Nanotubes

An experimental program was developed to evaluate the effect of multi-walled carbon nanotubes (MWCNTs) inclusion on elevated temperature properties of normal weight concrete (NWC) and lightweight concrete (LWC). The mechanical performance was assessed by conducting material property tests namely compressive strength (f’_c,_T), tensile strength (f’_t,T), mass loss (M_T), elastic modulus (E_T), compressive toughness (T_c) and stress–strain response under unstressed and residual conditions in the range of 23°C to 800°C. The mechanical properties were measured by heating 100?×?200 mm cylindrical specimens to 200°C, 400°C, 600°C and 800°C at a heating rate of 5°C/min. Results show that the inclusion MWCNTs in cementitious matrices enhanced the fire endurance. The relative retention of mechanical strength and mass of concretes modified with MWCNTs was higher. The stress–strain response of specimens modified with MWCNTs was more ductile. Microstructural study of cyrofractured samples evidenced the homogenous dispersion of nano-reinforcements in host matrix. Furthermore, the data obtained from high temperature material property tests was utilized to develop mathematical relationships for expressing mechanical properties of modified mixes as a function of temperature.     

The Effects of Non-uniform Temperature Distribution on Neutral Plane Level in Non-adiabatic High-Rise Shafts During Fires

The location of neutral plane level (NPL) of a high-rise shaft is an important factor for the evaluation of risks of smoke spreads in high-rise buildings, where the shaft internal pressure is equal to that of the building floor at the same height. The current method to determine the location of NPL assumes uniform temperature distribution inside a shaft, which causes concerns over accuracy of the predicted NPL for high-rise shafts with non-uniformly distributed temperatures during fires. To address the effect of temperature distribution on NPL location, this paper introduces a method to calculate temperature distribution and its associated NPL location based on a coupled model of smoke temperature profile, flow rate and pressure distribution inside a shaft. The measured data from a 1/3 scale experiment is used to validate the method and used to develop two empirical equations for NPL locations in terms of dimensionless numbers: one empirical equation based on shaft top temperature and the second based on shaft bottom temperature. A sensitivity study of the empirical equations is then conducted to evaluate the applicability of the developed equations when compared to the existing NPL method. It was found that for the existing NPL equation based on uniform temperature assumption may under-/overestimate the NPL locations, and the NRMSE would be over 50%, while the NRMSE of the empirical equation is only around 6% based on the results of coupled equations. For non-adiabatic shafts, the effects of non-uniform temperature distribution on NPL should be considered and the suggested empirical equations can predict NPL locations with a reasonable accuracy.     

复式钢管混凝土偏压柱试验

通过对9个不同尺寸和壁厚的内圆外方的复式钢管混凝土柱试件(其中内(圆)增强方钢管混凝土试件6个,方中空夹层钢管混凝土试件3个),进行偏压试验得到极限承载力和荷载-变形曲线。试验表明,对内(圆)增强方钢管混凝土,内置圆钢管的存在能够对偏压方钢管内核心混凝土起增强作用,且这种增强作用随着圆管管径的增大愈加明显;对于方中空夹层复式钢管混凝土偏压短柱,随着圆钢管管径的增加,其承载力降低的程度愈大。     

At home in generic places: personalizing strategies of the mobile rich

In the literature it is often suggested that mobile people, like their non-mobile counterparts, look for particular places to connect with. This has been documented in research focused on the way in which migrants (re)create particular places in their countries of destination (i.e., the formation of ethnic enclaves). However, our extensive fieldwork among Mexican professionals in Madrid, such as postgraduate students, academics, IT professionals, journalists, and others, point toward the opposite direction: for the very mobile and the recently arrived particular places matter little (Duyvendak in The politics of home. Belonging and nostalgia in Western Europe and the United States. Palgrave Macmillan, London, 2011; Ley-Cervantes in Stuck in the middle: home-making strategies of Mexican Middling Migrants. Ph.D. Thesis, Autonomous University of Madrid, 2012). Instead they rely on generic places, such as airports, chain restaurants or hotels to feel at home. Instead of taking for granted the homeliness of certain places, this paper aims to inquire the role of generic places in the home-making experiences of a small and rather privileged portion of the moving population.     

Monitoring the quality of mineral bottled water concerning to potential pathogenic bacteria and nitrate levels

The diversity of cultured pathogenic bacteria in the bottled mineral water (BMW) was investigated using selective media. The pure isolates from these selective media, which showed hemolytic activity on the blood agar media and antibiotic resistance, were identified by 16S rRNA gene technique. The seven obtained strains were belonged to the genus Pseudomonas, Bacillus, Acinetobacter, Stenotrophomonas, and Exiguobacterium, and were mostly closed to the pathogenic strains. The increasing of ozone concentration from air-fed ozone generators eliminate the growth of bacteria included the pathogenic bacteria, but in other side it increases the amount of nitrates and nitrites in the final product of the BMW. These findings revealed that the BMW either has potential pathogenic bacteria or high levels of nitrates and all these products may effect on the health of the end user.