PSI - Issue 5

Tiago Mendonça et al. / Procedia Structural Integrity 5 (2017) 48–54 Mafalda Monteiro et al. / Structural Integrity Procedia 00 (2017) 000 – 000

53

6

3. Repair and strengthening solutions

The main constraints to the rehabilitation of these bridges, that are very restrictive for the solutions to be applied, are their geometry and aesthetics and the materials used, namely, non-weldable rotary iron, the riveted sections, which require a thorough intervention, and the foundations of masonry, whose integrity is only guaranteed with the friction between its blocks. The principal objective of each solution of rehabilitation was the requalification of the road crossing and the correction of the anomalies of the bridge to extend even more its lifespan. Repair works included the following tasks:  Restorations and straighten of steel elements and connection joints, sometimes requiring the addition of new compatible material, and application of protective coating to suite environmental aggressiveness;  Pickling, in some cases substitution, of cover plates, inner plates, gussets and other connection plates;  Sealing of gaps with mastic and epoxy resins (Fig. 4);  Replacement of rivets and changing bastard screws with new rivets to respect aesthetics and original design;  Lubrication and repositioning of support devices and bearings, among others;  Sealing of slits in masonry walls with appropriate mortar or with injection of compatible slurry cement;  Reconstruction of reinforced concrete sections;  Protection of the river bed with rock fill layers around piers and abutments;

Fig. 4. Repair works: a) correction of flange buckling and rust bags, b) .substitution or addition of rivets, c) addition of new material to replace damaged sections.

Strengthening works were defined through structural analysis – 3D models of finite elements of beam and slab (Fig. 5). The global models were calibrated with the results of material tests and other information obtained from complementary studies (eg geotechnical survey). Beam sections of the model were reduced taking into account the loss due to corrosion. Security design checks were performed for regulatory actions in accordance with current Portuguese standards and European codes. In general, deck structural problems are due to buckling of elements as their high slenderness is insufficient to the level of compression installed. As the section itself has the necessary quantity of material to resist stresses the solution is to either reduce buckling length or reduce slenderness by adding material. In Abrantes Bridge the external pre-stress system had to be replaced. The same solution was adopted in Belver Bridge to deal with the increase of permanent loads of the new platform. These bridges are still waiting for works to start. None of the three bridges had resistance to seismic action. Masonry piers have stiffness far superior to its resistance. The seismic response of the pier itself is far higher than the one exclusively due to the deck mass. This means that masonry sections along pier could decompress, might drop and the structure collapse. Where differential settlements or insufficient supporting soil capacity were detected the solution was to execute micro-piles or jet-grouting columns with inner reinforcement. The resistance of piers was in some cases improved with encasing solutions with reinforcement. The seismic force was distributed among all the piers with high dynamic rubber bearing - HDRB type (damping devices). This devices permit to lower the structure response without restraints