Deck Connections

The role of anchorages and bearings in investigating the response of decks under wave forces has recently been highlighted by some notable studies. Table 2-4 presents the details and responses of deck connections for bridges under extreme waves. Lehrman (2010) and

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Lehrman et al. (2011) studied the behaviour of steel anchors on AASHTO girders using static and dynamic loadings. The loading cases adopted were static uplift, static drag, combined static uplift and drag, and combined dynamic uplift and drag. In the combined loading cases, the magnitude of static uplift was twice the drag force. The results showed that in combined loading cases, the drag force provided a compressive effect that increased the uplift capacity of the connections. Further, a numerical approach was suggested by Salem et al. (2014, 2016) using the discrete cracking method to capture the movement of decks under tsunami-generated wave forces. The bearing connection was modelled using two plates, at the top (sole) and bottom (bed), attached together using a friction coefficient of 0.6. Two blocks were fixed at the sides of the bearing plates to prevent their lateral movement. The velocity was assumed to have a linear increase with the percentage of air entrapment. This linear increase is up to a velocity of 3.13 m/s, which corresponds to air entrapment over the full depth of the girders. In addition, the drag force applied on the deck was adjusted to take into account the change in wave velocity due to the movement of the deck. The lateral movement of decks was found to occur at air entrapment of 75% and 100% of the girder’s depth. More recently, the forces in flexible and rigid support bearings were studied by Cai et al. (2017). The flexible bearing was modelled using non-linear vertical spring elements, whereas the rigid bearing supports were modelled using linear elements. In the flexible deck, the onshore girder bearing was kept vertically rigid to initiate the rotation. It was reported that the deck rotation is mainly related to drag forces. The peak rotating moment was found to occur in an opposite direction to that recommended by the AASHTO (2008) equations. In addition, the bearings showed high tensile and compressive stresses at an inundation ratio of -0.5. Cai et al. (2017) reported that the maximum uplift movement of the deck corresponded to the case where the water level was at the girder soffit (zero

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clearance). In contrast, the study discussed above by Ataei and Padgett (2015b) concluded that for the same case, maximum lateral displacements occur. Furthermore, a comparative study was conducted by Ataei (2013) on the effectiveness of shear keys, restrainer cables and high-strength bars for preventing large displacements of the deck. Shear keys were found to be the most effective measure for preventing lateral displacement without significant force transfer to the substructure. The lateral movement of the deck was reduced by up to 11 times, but this led to an increase in uplift force by about 60%. Furthermore, non-linear static analyses that adopt simplified load patterns distributed over vertical elements have recently been implemented in frame structures to provide an adequate evaluation of the structural response. Further discussion on the load patterns, load discretization methods and pushover analyses for structures subjected to extreme waves can be found in Refs. AASHTO (2008); Alam et al. (2017); Ataei and Padgett (2013b); FEMA (2008); Foytong et al. (2013); Foytong et al. (2015); Fukuyama et al. (2011); Macabuag and Rossetto (2014); Macabuaget al. (2014); Nanayakkara and Dias (2016); Petrone et al. (2017).

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Table 2-4. Details and response of deck connections in recent investigations for bridges subjected to extreme wave forces.

Connection Details Response/failure Remarks/details Reference

Clip bolt Steel angle (mm): 203×152×25

Connected to bottom flange using four bolts inserted into pre-fabricated threads.

Static uplift and drag: separation of concrete around the strands.

Combined uplift and drag: external strands appeared along 610 mm of girder and pullout of inserts was observed at flanges.

Has lowest capacity compared to headed stud and through-bolt.

Lehrman (2010), Lehrman et al. (2011) Headed stud Steel plate positioned at bottom of girder

with welded headed stud anchor 16 mm in diameter and 152 mm long. Plate connected to substructure by expansion anchor.

Static uplift: yielding and rupture of both stud and plate.

Static drag: plate underwent plastic deformations without slip in strand. Combined uplift and drag: fracture of seaward stud.

Connection has greatest strength. Yielding failure can be utilized in practical design of connection to limit transfer of forces to substructure.

Through-bolt Steel angle (mm): 203×152×25

Connected to bottom flange using two 25 mm diameter bolts.

Static uplift: initiation of cracks and strand slip. Cracks further propagated at girder soffit until exposure of strands.

Static drag: further increase in capacity due to compressive effect of uplift forces at seaward side.

Combined uplift and drag: cracks at bolt locations after exceeding self-weight of girder.

Combined cyclic uplift and drag: significant cracks and banding followed by pull down of prestressing strands.

Compression from drag enables connection to sustain higher loads under combined static loads. Large increase in deformation at small change in load due to rapid propagation of crack from seaward to landward side at combined static loads.

Connection failed due to combined tension from uplift and drag.

Fixed and movable bearing

Bottom and top plates with specified contact friction. Friction coefficient zero for movable bearing and 0.6 for fixed bearing. Lateral movement prevented using bolts fixed at sides.

All simply-supported decks on bearings showed overturning and sliding failure modes.

Bearing plates experienced failure due to movement of side block and top plate. Salem et al. (2014, 2016) Bearing fixed and movable

First deck modelled to allow movement in horizontal direction only. Linear vertical spring elements used to model girder

Ultimate vertical displacement of deck occurs at zero clearance.

Positive (clockwise) overturning moment was found to be the ultimate moment, which contradicts

Cai et al. (2017)

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direction

support. Spring elements can deform in tension and compression.

Second deck modelled with linear vertical spring elements only at last girder at onshore side of deck. Non-linear vertical spring elements used for rest of girders, which can deform only in compression. This model allows both rotation and horizontal movement of deck.

At inundation ratio of -0.5, larger uplift force and lower moment in interaction diagram (moment-uplift force) observed. Bearings show high tensile and compressive stresses. At inundation ratio of 0.5, negative moment occurs.

AASHTO (AASHTO, 2008) method which assumes that negative moment is the ultimate.

Simplified interface friction

Interface coefficient of friction of 0.6 used between deck and substructure.

High deck vertical displacements at larger inundation accompanied by larger moments and rotations.

Horizontal displacements are high at zero clearance.

Resistance of deck to horizontal movement reduces with uplift movement.

Ataei and Padgett (2015b)

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