Bolting

BATUKAWA BRIDGE EXTENSION (QUALITY ASSURRANCE ENGINEER-ALSON CHIN)

BOLTING The tightening of HSFG bolts can be done by either of the following methods: 1. Turn-of-nut tightening method: In this method the bolts are first made snug tight and then turned by specific amounts (usually either half or three-fourth turns) to induce tension equal to the proof load. 2. Calibrated wrench tightening method: In this method the bolts are tightened by a wrench calibrated to produce the required tension. 3. Direct tension indicator(DTI) method: In this method special washers with protrusions are used .As the bolt is tightened, these protrusions are compressed and the gap produced by them gets reduced in proportion to the load. This gap is measured by means of a feeler gauge, consisting of small bits of steel plates of varying thickness, which can be inserted into the gap. Orange silicone

Grade of bolt ASTM Grade10.9

Curved Protrusions

The DTI comes with the bolts, nuts; harden washer and the DTI

BATUKAWA BRIDGE EXTENSION (QUALITY ASSURRANCE ENGINEER-ALSON CHIN)

DTI INSTALLATION 1. Snug tighten the joint Always snug tighten an array of „Squirter®‟ DTI assemblies in a joint before final tightening. Starting from the middle of the joint, tighten the assemblies in a staggered pattern working outwards and partially tighten without any or much silicone showing. Don‟t fully compress the „Squirter®‟ DTI on the snug (first) pass. After snug tightening there should be no (or very little) silicone showing.

2. Finally tighten the joint Tighten the „Squirter®‟ DTI assemblies, in the same pattern as for snug tightening until after the orange silicone appears in volume from most of the „Squirters®‟ squirt locations. Don‟t stop tightening until the squirt volume and appearance is just like it was in the calibration exercise. Then stop tightening.

3. Inspection Observe the „Squirter®‟ DTI‟s calibration procedure at the beginning of the project. Ensure the DTI gap has been closed sufficiently at the intended squirt appearance. Inspectors will then be able to tell at a glance which of the bolts has been tensioned correctly. Occasional checks with a feeler gauge may be carried out.

BATUKAWA BRIDGE EXTENSION (QUALITY ASSURRANCE ENGINEER-ALSON CHIN)

DTI INSPECTION The DTI installation can be either at end of the bolt. Just make sure the DTI bumps bear against the underside of the bolt head or against a hardened flat washer, never directly against the nut or the steel plates. These are available free issue from Applied Bolting and are in every keg. Have some .015" and/or some .005" feeler gages available which will fit into the openings of the DTI between the DTI bumps.

BATUKAWA BRIDGE EXTENSION (QUALITY ASSURRANCE ENGINEER-ALSON CHIN) SPLICE JOINTS CONNECTION / INSTALLATION

A bolted field splice is designed as a slip critical connection. This type of connection relies on the clamping force provided by the bolts in tension and the friction between the plies. It is critical that splice plates, and beam or girder ends, are kept free from debris and oil which would change the friction coefficient between the plies. The correct tension in the bolts is achieved by proper bolting techniques and measured by specialized load cell washers called direct tension indicators (DTIs) which compress at a given bolt tension force.

Drift Pins

Wrench

DTIs

The fit-up or erection bolts and drift pins are used together during fit-up and are removed and replaced with production bolts in a systematic manner, but only after the splice has the remainder of its holes filled with production bolts in a fully tightened condition. The splice plates have to provide enough clamping force to prevent slip at all times while the member is in its final location on the bridge.

BATUKAWA BRIDGE EXTENSION (QUALITY ASSURRANCE ENGINEER-ALSON CHIN)

Stage 1: Centralized the connection by using drift pins and hoisting by the mobile crane. Aligning edge girders, pinning and bolting splice plate.

Drift pins

Drift pins

Stage 2: Snug tighten an array of DTI assemblies in a joint before final tightening and starting from the middle of the joint, tighten the assemblies in a staggered pattern working outwards and partially tighten without any or much silicone shows.

BATUKAWA BRIDGE EXTENSION (QUALITY ASSURRANCE ENGINEER-ALSON CHIN)

Stage 3: Tighten the DTI assemblies, in the same pattern as for snug tightening until after the orange silicone appears in volume. Then stop tightening.

Stage 4: Inspected by inserted the 0.05” feeler gage into half the gaps between the DTI bumps. Don‟t try to use the feeler gage so much, judge the gaps closure mainly by eyes. A completely “flattened” DTI is okay.

BATUKAWA BRIDGE EXTENSION (QUALITY ASSURRANCE ENGINEER-ALSON CHIN)

FORCE TRANSFER MECHANISM In this section the force transfer mechanisms of bearing and friction type of bolted connections are described. Force transfer by shear in bolts The free body diagram of the shear force transfer in bearing type of bolted connection. It is seen that tension in one plate is equilibrated by the bearing stress between the bolt and the hole in the plate. Since there is a clearance between the bolt and the hole in which it is fitted, the bearing stress is mobilised only after the plates slip relative to one another and start bearing on the bolt. The section x-x in the bolt is critical section for shear. Since it is a lap joint there is only one critical section in shear (single shear) in the bolt. In the case of butt splices there would be two critical sections in the bolt in shear (double shear), corresponding to the two cover plates.

The free body diagram of an HSFG connection It can be seen that the pretension in the bolt causes clamping forces between the plates even before the external load is applied. When the external load is applied, the tendency of two plates to slip against one another is resisted by the friction between the plates. The frictional resistance is equal to the coefficient of friction multiplied by the normal clamping force between the plates.

Until the externally applied force exceeds this frictional resistance the relative slip between the plates is prevented. The HSFG connections are designed such that under service load the force does not exceed the frictional resistance so that the relative slip is avoided during service. When the external force exceeds the frictional resistance the plates slip until the bolts come into contact with the plate and start bearing against the hole. Beyond this point the external force is resisted by the combined action of the frictional resistance and the bearing resistance.