03-23-2011, 02:27 AM
Hi guys. Just a few thoughts in relation to this topic.
Bridge Bearings are described by Engineers [Civil or Structural] as fixed or rolling, and no matter if steel or concrete they are made with allowances for casting errors in the abutment formwork as well as expansion and contraction due to temperature fluctuations and different rates of movement between materials.
Formwork is often [only half ] jokingly described as the stuff used to slow concrete down. When I was an apprentice Carpenter [back in '85] I witnessed firsthand the result of formwork failing under the pressure of wet [also decribed as plastic] concrete and the resultant mess. Often the bottom edges or other awkward parts of the formwork shuttering [the face against the wet concrete] can bow outward under the immense pressures involved. The wet concrete can also spread over [partially or totally ] bearing or anchoring plates and push or submerge Holding Down Bolts used to connect items to the finished concrete structure.
Bridge Beams and often sub-road support panels are now days Pre-Cast in factory settings either at the site in a temporary factory or at an established Pre-Cast factory. These components can then be either pre or post tensioned as specified by the Structural Engineer, where by the steel reinforcing inside the beam is tensioned before the loading develops to reduce sagging and cracking under load.
I would expect that where the concrete bridge beams rest on the abutments, that the actual surface of the beam and also the abutment will have a [probably galvanised] steel facing plate to deal with the enormous surface stresses and friction forces imposed on the contact points.
Here endeth the Bridge Bearing Primer 101
Mark
Bridge Bearings are described by Engineers [Civil or Structural] as fixed or rolling, and no matter if steel or concrete they are made with allowances for casting errors in the abutment formwork as well as expansion and contraction due to temperature fluctuations and different rates of movement between materials.
Formwork is often [only half ] jokingly described as the stuff used to slow concrete down. When I was an apprentice Carpenter [back in '85] I witnessed firsthand the result of formwork failing under the pressure of wet [also decribed as plastic] concrete and the resultant mess. Often the bottom edges or other awkward parts of the formwork shuttering [the face against the wet concrete] can bow outward under the immense pressures involved. The wet concrete can also spread over [partially or totally ] bearing or anchoring plates and push or submerge Holding Down Bolts used to connect items to the finished concrete structure.
Bridge Beams and often sub-road support panels are now days Pre-Cast in factory settings either at the site in a temporary factory or at an established Pre-Cast factory. These components can then be either pre or post tensioned as specified by the Structural Engineer, where by the steel reinforcing inside the beam is tensioned before the loading develops to reduce sagging and cracking under load.
I would expect that where the concrete bridge beams rest on the abutments, that the actual surface of the beam and also the abutment will have a [probably galvanised] steel facing plate to deal with the enormous surface stresses and friction forces imposed on the contact points.
Here endeth the Bridge Bearing Primer 101
Mark
Fake It till you Make It, then Fake It some More