Olivier Burdet

Punching Tests of Slabs with Low Reinforcement Ratios

Vcal, kN Vt /Vcal Eq. (4b) fu /fy PG-1 260 210 1.50 573/656 27.6/34.5 1023 1.72 1.028 — 1045 0.979 PG-2b 260 210 0.25 552/612 40.5/50.6 440 0.19 — 1.109 365 1.205 PG-4 260 210 0.25 541/603 32.2/40.2 408 0.23 — 1.115 373 1.094 PG-5 260 210 0.33 555/659 29.3/36.6 550 0.35 — 1.187 495 1.111 PG-10 260 210 0.33 577/648 28.5/35.6 540 0.37 — 1.123 490 1.102 PG-11 260 210 0.75 570/684 31.5/39.4 763 0.75 1.163 — 833 0.916 PG-3 520 456 0.33 520/607 32.4/40.5 2153 0.29 — 1.167 1876 1.148 PG-6 130 96 1.50 526/607 34.7/43.4 238 1.25 1.075 — 268 0.888 PG-7 130 100 0.75 550/623 34.7/43.4 241 0.66 1.133 — 212 1.137 PG-8 130 117 0.28 525/586 34.7/43.4 140 0.23 — 1.116 131 1.069 PG-9 130 117 0.22 525/586 34.7/43.4 115 0.19 — 1.116 108 1.065 Average ratio 1.065 Standard deviation 0.089

Ultrasonic measurements and static load tests in bridge evaluation

Abstract The cross-sectional stiffness of a bridge depends on one hand on its geometry and on the other hand on its material properties. The inclusion in the stiffness of ‘nonstructural’ elements such as parapets or asphalt layers leads to better estimates of deflections under the load test. The most important unknown variable remains however the concretes modulus of elasticity. Ultrasonic measurements offer a cost-effective and nondestructive alternative for the determination of the modulus of elasticity of concrete in an existing structure. A computerized database was established to investigate the actual behaviour of bridges subjected to a load test. The database currently contains the results of over 200 load tests carried out by our institute, along with the geometry of the bridges. Ultrasonic measurements are currently being used to determine the actual modulus of elasticity of these bridges, with the purpose of better understanding the behaviour of structures subjected to short term loads. Drilled cores were taken from a limited number of bridges and the modulus of elasticity of cores is compared with the modulus predicted by the ultrasonic measurements. A case study showing the evolution of the modulus of elasticity of the Aubonne bridge determined by these various methods is presented.

Effect of duct type on shear strength of thin webs

A series of 16 specimens of concrete web panels 23.6 x 23.6 x 4.9 in. (600 x 600 x 125 mm) was tested in compression to investigate the effect of the presence of various types of post-tensioning ducts on the strength of the shear-induced compression struts. Most panels were cast in the laboratory, but some were extracted from an actual bridge girder, which had been previously loaded, allowing investigation of the effect of web cracking on the ultimate strength. The presence of a duct in a web, whether injected or not, decreases the compressive strength of the panel. This effect is most pronounced for non-injected ducts, but is also much larger for injected plastic ducts than for injected steel ducts. The effect of web cracking further decreases the strength of web panels containing post-tensioning ducts, and this effect can be estimated using classical strength reduction formulas.

Automatic Monitoring of Bridges using Electronic Inclinometers

The paper presents a new method for the automatic monitoring of bridges deformations. Based on the use of electronic high precision inclinometers, this method permits to accurately reconstruct the deflected shape of the bridge and to follow its long-term evolution. A practical and efficient method for the reconstruction of the deflected shape from measured rotations is proposed. The example of an actual bridge in Western Switzerland, in which the system is operational, is described. The results obtained correspond well with those obtained from independent measurements.

Transition Slabs of Integral Abutment Bridges

Abstract Over the past decades, an increasing number of bridges with integral abutment have been built in Switzerland. This type of bridge offers various advantages over standard bridges with abutments, equipped with expansion joints and bearings that require regular inspection and maintenance. One main concern of integral abutment bridges is related to the soil-structure interaction, in particular between the transition slab and the embankment. To avoid any expansion joints, transition slabs are directly connected to the end of integral abutment bridges. They are therefore subject to large displacements of the bridge deck due to temperature effects and creep and shrinkage in concrete bridges. Consequently, detailing of transition slabs needs to be carefully considered. This paper investigates the behaviour of transition slabs, focusing on the settlement of the pavement at the end of the transition slab and on the cracking of the pavement between the bridge deck and transition slab. On that basis, a modified geometry of the transition slab and a new detail for the connection between the bridge deck and the transition slab are proposed. If these propositions are considered at an early stage in the design process, they will result in an improved long term performance of bridges with integral abutments without increasing the construction costs.

DESIGN OF A CURVED INCREMENTALLY LAUNCHED BRIDGE

Using the example of the Ile Falcon Bridge, it is shown that, given proper attention during design and rigorous quality control during construction, incremental launching can be used successfully f...

Thermal effects in the Long-Term Monitoring of Bridges

Daily and seasonal temperature variations induce deflections of bridges. The amplitude of these moments is significant in comparison with the yearly increment caused by irreversible long-term deflections. To improve the quality of the interpretation of monitoring measurements, thermal movements thus need to be taken into account in the long-term monitoring of bridge deflections. The paper presents the results of the long-term monitoring of deflections of several bridges in Switzerland over the past 20 years, with a particular attention given to thermal effects. The daily and seasonal movements of bridges under thermal effects are shown. The correlation between the measured temperatures and gradients and the position of bridge is shown, and methods to compensate for thermal effects are outlined. This allows to filter out the largest part of the thermal effects and to make more accurate assessments of the actual irreversible deformations. The significant influence of temperature on the measurement results is illustrated on the basis of a large number of manual measurements by hydrostatic leveling and automatic measurements by electronic inclinometers. The simultaneous measurement of the ambient temperature and of the temperature of the concrete of the bridge itself gives useful information to take thermal effects into account.

Comparison of Internal and External Prestressing for Typical Highway Bridges

Summary The paper presents an analytical comparison of the amount of prestressing required for two similar bridges, one with internal and the other with external prestressing. This comparison shows that bridges with external prestressing can become economically competitive for large girder depths. The detrimental effect of the smaller stress in the prestressing steel at the ultimate limit state is more than compensated by the thinner webs made possible by the absence of ducts.