L.F. Boswell

A field deployable, multiplexed Bragg grating sensor system used in an extensive highway bridge monitoring evaluation tests

A multiplexed optical fiber Bragg grating sensor system with a measurement bandwidth of up to 200 Hz enabling dynamic loading events, e.g., road traffic, to be observed has been designed, installed, and tested over an 18-month period on a 346-m road bridge in Norway, for design verification and structural integrity monitoring purposes. A network of 32 fiber Bragg sensors was surface bonded along with a corresponding set of resistive strain gauges for comparative tests to be made. The wavelength data were calibrated against two thermally stabilized (/spl sim/0.15 pm) reference gratings, which rejected common mode noise and provided absolute wavelength scaling. These data provides independent strain and temperature information. Long-term test results showed good linearity and repeatability of <10 /spl mu//spl epsiv/ over the test period with a precision of /spl plusmn/5 /spl mu//spl epsiv/ and a resolution of /spl plusmn/1 /spl mu//spl epsiv/. The readings from the FBG sensors were comparable to those from the foil gauge sensors to within /spl plusmn/4 /spl mu//spl epsiv/.

Behaviour of double skin composite construction

Abstract Double Skin Composite (DSC) or Steel–Concrete–Steel sandwich construction was first conceived over 14 years ago for use in submerged tube-tunnel construction in the UK [1] . More recently, British Steel plc (now Corus UK) have developed the original shear-stud concept to currently friction-weld round steel bars to both plates in a simultaneous operation. This process not only makes the units easy to handle, but also provides sufficient strength to resist the internal hydrostatic pressures due to fresh concrete. This product is called Bi-Steel. This paper outlines a programme of research conducted at City University, in which the elastic and plastic behaviour of a series of 16 large-scale, simply supported, three-point bending tests were investigated [2] . These tests compare existing and new construction methods, and were conducted until collapse due to local buckling of the compression plate. The test programme is supported by a series of analytical solutions covering the elastic and plastic performance of the specimens.

Incorporation of fiber-optic sensors in concrete specimens: testing and evaluation

As series of tests has been carried out on the performance of several fiber-optic temperature sensors, operating on the fluorescence lifetime principle using neodymium-doped fiber and configured into ruggedized temperature probes, mounted in a number of different concrete samples. The aim has been to evaluate the performance of probes fitted into concrete specimens to simulate the conditions experienced in structures used in civil applications, such as bridges and dams. A key feature of the investigation was observing the integrity of the sensors under investigation while obtaining temperature data from the device. The results show the sensors operated well from below room temperature to beyond 300/spl deg/C, preserving their integrity under adverse test conditions.

THE FATIGUE STRENGTH OF GROUTED REPAIRED TUBULAR MEMBERS

The results of fatigue tests performed on bolted split-sleeve grouted clamps of the type used to repair or strengthen tubular members are reported. Sinusoidal tension-compression axial loading was employed; the applied load and the grout age were the variables. The results indicate that the margin of safety against fatigue may not be as great as expected, with some results close to the factored design loads. It is suggested that particular attention should therefore be paid to the fatigue performance of bolted grout-filled clamps in service.