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CONTENTS
Volume 10, Number 6, November 2007
 

Abstract
Wind pressure data have been collected on the tiled roof of a full-scale test house at Silsoe in the UK. The tiled roof was of conventional UK construction with a batten-space and bitumen-felt underlay beneath the interlocking concrete tiles. Pressures were monitored on the outer surface of selected tiles, at several locations within the batten-space, and beneath the underlay. Data were collected both with and without ventilator tiles installed on the roof. Little information appears to exist on the share of wind load between tiles and underlays which creates uncertainty in the design of both components. The present study has found that for the critical design case of maximum uplifts it would be appropriate to assign 85% of the net roof load to the tiles and 15% to the underlay when an internal pressure coefficient of -0.3 is used, and to assign 60% to the tiles and 50% to the underlay when an internal pressure coefficient of +0.2 is assumed (an element of design conservatism is inherent in the apparent 110% net loading indicated by the latter pair of percentage values). These findings indicate that compared with loads implied by BS 6399-2, UK design loads for underlay are currently conservative by 25% whilst tile loads are unconservative by around 20% in ridge and general regions and by around 45% in edge regions on average over roof slopes of 15o-60o.

Key Words
felt; house; permeable-cladding; slates; tiles; twin-skin; pressures; roofs; underlay; UK construction; wind-loads.

Address
A. P. Robertson? and R. P. Hoxey; University of Birmingham, WrestPark, Silsoe, Bedford MK45 4HR, UK
N. M. Rideout; Building Product Design Ltd, North Frith Oasts, Ashes Lane, Hadlow, Kent TN11 9QU, UK
P. Freathy; RWDI Anemos, Unit 4, Lawrence Industrial Estate, Lawrence Way, Dunstable, Beds LU16 1BD, UK

Abstract
The present study aims to generate turbulent inflow data to more accurately represent the turbulent flow around a square cylinder when the inflow turbulence level is significant. The modified random flow generation (RFG) technique in conjunction with a previously developed LES code is successfully adopted into a finite element based fluid flow solver to generate the required inflow turbulence boundary conditions for the three-dimensional (3-D) LES computations of transitional turbulent flow around a square cylinder at Reynolds number of 22,000. The near wall region is modelled without using wall approximate conditions and a wall damping coefficient is introduced into the calculation of sub-grid length scale in the boundary layer of the cylinder wall. The numerical results obtained from simulations are compared with each other and with the experimental data for different inflow turbulence boundary conditions in order to discuss the issues such as the synthetic inflow turbulence effects on the 3-D transitional flow behaviour in the near wake and the free shear layer, the basic mechanism by which stream turbulence interacts with the mean flow over the cylinder body and the prediction of integral flow parameters. The comparison among the LES results with and without inflow turbulence and the experimental data emphasizes that the turbulent inflow data generated by the present RFG technique for the LES computation can be a viable approach in accurately predicting the effects of inflow turbulence on the near wake turbulent flow characteristics around a bluff body.

Key Words
computational methods; random flow generation (RFG) algorithm; turbulence; large eddy simulation (LES); square cylinder; inflow turbulence.

Address
M. Tutar; Mersin University, Department of Mechanical Engineering, Ciftlikkoy, 33343, Mersin, Turkey
I. Celik; West Virginia University, Department of Mechanical and Aerospace Engineering, Morgantown, WV 26506-6106, USA

Abstract
The cable-stayed-suspension hybrid bridge is a cooperative system of the cable-stayed bridge and suspension bridge, and takes some advantages and also makes up some deficiencies of both the two bridge systems, and therefore becomes strong in spanning. By taking the cable-stayed-suspension hybrid bridge, suspension bridge and cable-stayed bridge with main span of 1400 m as examples, the mechanics performance including the static and dynamic characteristics, the aerostatic and aerodynamic stability etc is investigated by 3D nonlinear analysis. The results show that as compared to the suspension bridge and cable-stayed bridge, the cable-stayed-suspension hybrid bridge has greater structural stiffness, less internal forces and better wind stability, and is favorable to be used in super long-span bridges.

Key Words
cable-stayed-suspension hybrid bridge; suspension bridge; cable-stayed bridge; mechanics performance.

Address
Xin-Jun Zhang; College of Civil Engineering and Architecture, Zhejiang University of Technology, Hangzhou 310032, P.R. China

Abstract
The suspension bridge is situated in an area of complex topography with both open sea and overland turbulence characteristics, and it is subject to frequent typhoon occurrences. This paper investigates experimentally the possible vortex shedding events of the structure under high wind and typhoon conditions. A single-degree-of-freedom model for the vibration of a unit bridge deck section is adopted to determine the amplitude of vibration and to estimate the parameters related to the lifting force in a vortex shedding event. The results of the studies are presented in a companion paper (Law, et al. 2007). In this paper, statistical analysis on the measured responses of the bridge deck shows that the vibration response at the first torsional mode of the structure has a significant increase at and beyond the critical wind speed for vortex shedding as noted in the wind tunnel tests on a section model of the structure.

Key Words
wind; typhoon; dynamic; vortex shedding; suspension bridge; steel; traffic; model; optimization.

Address
S. S. Law; Civil and Structural Engineering Department, Hong Kong Polytechnic University, Hong Kong, People?s Republic of China.
Q. S. Yang; Bridge Engineering Department, Beijing Jiao Tung University, People?s Republic of China.
Y. L. Fang; Mechanical Engineering Department, Tai Yuen University, People?s Republic of China.

Abstract
Statistical analysis on the measured responses of a suspension bridge deck (Law, et al. 2007) show that vibration response at the first torsional mode of the structure has a significant increase at and beyond the critical wind speed for vortex shedding as noted in the wind tunnel tests on a sectional model. This paper further analyzes the measured responses of the structure when under typhoon conditions for any possible vortex shedding events. Parameters related to the lifting force in such a possible event and the vibration amplitudes are estimated with a single-degree-of-freedom model of the system. The spatial correlation of vortex shedding along the bridge span is also investigated. Possible vortex shedding events are found at both the first torsional and second vertical modes with the root-mean-square amplitudes comparable to those predicted from wind tunnel tests. Small negative stiffness due to wind effects is observed in isolated events that last for a short duration, but the aerodynamic damping exhibits either positive or negative values when the vertical angle of wind incidence is beyond ?10o. Vibration of the bridge deck is highly correlated in the events at least in the middle one-third of the main span.

Key Words
wind; typhoon; dynamic; vortex shedding; suspension bridge; steel; traffic; model; optimization.

Address
S. S. Law; Civil and Structural Engineering Department, Hong Kong Polytechnic University, Hong Kong, People?s Republic of China.
Q. S. Yang; Bridge Engineering Department, Beijing Jiao Tung University, People?s Republic of China.
Y. L. Fang; Mechanical Engineering Department, Tai Yuen University, People?s Republic of China.


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