Prepared and Presented bySr. Mech. InspectorAkram M. Megdad

Structural Steel Bolted JointsWhen Steel Structure Bolting has been designed, manufactured, installed and inspected according to Codes and specified Procedures, this will ensure structural integrity. But when any of these tasks fail to meet the job requirements, disaster could happen including the loss of human lives.

Structural Steel Bolted Joints1981 two suspended walkways within the atrium of the Kansas City Hyatt Regency Hotel collapsed, resulting in the death of 114 people The collapse was caused by failure of the connections between the hanger rods and the main-carrying box beams of the walkways.

In this presentation I will discuss the following topics. How Bolts WorkBolt FailuresConclusionBolt InspectionHigh Strength Steel BoltsStructural Steel Bolted Joints

Threaded fasteners are classified by shape, material and finish, which are specified by industry standards. In the United States, the American Society for Testing Materials (ASTM) sets the standards. In Europe, the International Standards Organization (ISO) sets the standards. Structural Steel Bolted Joints

Steel structural bolts are heavy hexagon head bolts having a controlled thread length intended for use in steel structural connection assemblies such as:BuildingsBridgesPipe RacksStructural Steel Bolted Joints

To keep steel structure connection joints together, high Applied force must be exerted on the joints, that is If connection joint needed 8,000 pounds of force to hold two plates together, any force applied to the plates that is less than 8,000 pounds would not be enough to separate the plates. How Bolts WorkStructural Steel Bolted JointsForce

It is often helpful to think of the bolt as a spring. It may seem odd to think of steel structure as being held together by a bunch of springs, but this analogy works to show what happens when a bolt is tightened. How Bolts WorkStructural Steel Bolted Joints

The clamping force Fc is the difference between the preload force Fp and the tension force Ft on the joint. The clamping force is what holds the parts together. This translates mathematically to:FcFpFt=-How Bolts WorkMathematically Structural Steel Bolted Joints

When a bolt is tightened, both tension and torsional stress is established within the bolt. This establishes a PRE-LOAD (clamping force) that is developed and applied to structural bolt connection assembly. is the technical term for the tension caused by tightening the fastener that holds the assembled parts together. PRE-LOADBolt Pre-LoadStructural Steel Bolted Joints

The bolt material strength is specified by the its "grade.For example : A grade 8 bolt is stronger than a grade 5, which is stronger than a grade 2. The grade is indicated by a series of marks on the bolts head Strengths of BoltsStructural Steel Bolted Joints

One important consideration for steel structure a bolt is its The alloy (example: cold working) Processing method (example: heat treating)Strength and is determined by: Strengths of BoltsStructural Steel Bolted Joints

Looking at the stress strain curve Tensile Strength sometimes called the ultimate strength, is the stress level where the material breaks Yield Strength is the stress level where the material yields or permanently deforms. Strength of BoltsStructural Steel Bolted Joints

Bolted joints are widely used in all types of steel structural connections, designed to operate under the expected loads without exceeding the yield stress of the material. Bolted joints offer many advantages over welded joints such as maintainability. However they are costly in that frequently additional parts are needed (washer, nut) compared to riveted or welded joints and they require more skill & effort to assemble. Bolted connectionsStructural Steel Bolted Joints

Bolted connectionsJoints required to resist shear between their connected parts are designated as eitherBearing-Type ConnectionsFriction-Type ConnectionsStructural Steel Bolted Joints

Bolted connectionsBearing Type Connection: In this joint, the load is transferred from the steel into the bolt by bearing against the shank of the bolt, carried through the bolt by shear, then into the next layer of steel by bearing of the bolt against the side of the bolt hole.Structural Steel Bolted Joints

Friction Type Connected are defined as joints which slip would be detrimental to the serviceability of the structure. They include::1. Joints subjected to fatigue loading. 2. Joints with bolts installed in oversized holes.3. Joints with bolts installed in slotted holes. 4. Joints subject to significant load reversal.5. Joints in which welds and bolts share in transmitting load at a common faying surface.6. Joints in which the engineer designated on the contract plan and specifications.Structural Steel Bolted Joints

Bolts InstallationBolts in connections not within the slip-critical category nor subject to tension loads nor required to be fully tensioned bearing type connections shall be installed in properly aligned holes, but need only be tightened to the Snug Tight Condition.Structural Steel Bolted Joints

The "snug tight condition" is defined as "the tightness attained by either a few hits of an impact wrench or the full effort of a worker with an ordinary spud wrench that brings the connected plies into firm contact" by the most recent AISC LRFD Specification (Dec. 1, 1993), Section J3.1. Snug Tied ConditionStructural Steel Bolted Joints

Bolts Installationsubject to direct tension, and fully pre-tensioned bearing connections fasteners, together with washers of size and quality specified, shall be installed in properly aligned holes and tightened to provided at least the minimum tension shown in table 4, section 8 (AISC ninth edition). By one of the following methods Structural Steel Bolted JointsSlip-Critical Connections,In

When Turn of the nut method used, a representative sample of not less than three bolts and nuts of each diameter, length and grade to be used shall be checked at the start of work in a device capable of indicating bolt tension not less than five percent greater than tension required.Following this initial operation all bolts in the connection shall be tightened further by the applicable amount of rotation specified in table 5 of (AISC section 8, ninth edition)Turn of the nut methodStructural Steel Bolted Joints

Bolt InstallationTightening of bolts using direct tension indicator is permitted provided the suitability of the device can be demonstrated by testing bolts sample table 5 of (AISC section 8, ninth edition)Direct tension indicatorStructural Steel Bolted Joints

Bolt InstallationCalibration wrench tightening may be used only when the installation procedures are calibrated on a daily basis. When this procedure is used, it shall be set to provide tension not less than 5% in excess of the minimum tension specified in table 4 of (AISC section 8, ninth edition). It shall be verified during actual installation in the assembled steel work that the wrench adjustment selected by the calibration does not produce a nut or bolt head rotation from snug tight greater than that permitted in table 5 of (AISC section 8, ninth edition). If manual torque wrenches are used, nut shall be turned in the tightening direction when torque is measured. Calibrated wrench tighteningStructural Steel Bolted Joints

In progress work6. Select a procedure properly use to tighten all bolts.2. Inspect the material (bolts, washers, nuts etc.)4. Verify equipment calibration documents.3. Observe the calibration procedure.5. Monitor bolt installation. Determine the job requirement.Structural Steel Bolted JointsInspector ResponsibilityInspector should :

Arbitration Inspection:When high strength bolts in slip-critical connection and connection subject to direct tension have been installed, the following arbitration procedures may be used.The inspector shall use a manual torque wrench to give an indication that the job inspecting torque has been reached.2. This specification does not recognize standard torques determined from tables or formulas.Structural Steel Bolted Joints3. Tightening beyond the initial condition must not produce greater nut rotation than 1 1/2 times that permitted in table 5. The job inspecting torque shall be taken as the average three value. 4. The inspecting wrench shall then be applied to the tightened bolts in the work to determine the torque necessarily to turn the nut of bolt head 5 degrees (approximately 1 inch at 12 inch radius).5. Bolts in the structure shall be 10% randomly checked, but not less than 2 bolts selected at random in each connection joint in question. If any nut or bolt is turned by the application of the job inspecting torque, all the bolts in the connection shall be rejected (then all the rejected bolts shall be tightened and reinspected). Inspector Responsibility

Delayed verification Inspection:If verification of bolt tension is required after a passage of a period of time and exposure of the completed joint, the arbitration inspection will provide indication of bolt tension which is of questionable accuracy. Procedures appropriate to the specific situation should be used for verification of bolt tension (this might involve use of the arbitration procedure or might require the development and sue of alternative procedures.Structural Steel Bolted JointsInspector Responsibility

Bolt FailureWhen a threaded fastener can not sustain the expected loading and becomes detached, a significant failure In structural connection may occur.Structural Steel Bolted Joints

Failure as a result of an overloadMetal FatigueImproper DesignFailure from improper torqueExamples of bolt failures that have been involved in serious losses. Bolt FailureStructural Steel Bolted Joints

Metal fatigue is the phenomenon characterized by progressive crack growth during cyclic loading. A crack is often initiated at a flaw or stress riser (sharp notch) in a part. repeated impact cause the crack to increase in size until the part can no longer sustain the load, and a final fracture occurs. Bolt FailureMetal FatigueStructural Steel Bolted Joints

Wear on the bolt threads is the result of bolt movement due to insufficient clamping force. Bolt FailureImproper DesignStructural Steel Bolted Joints

Bolt FailureThis is a view of a bolt that fractured in the threaded area. The 45 degree full-slant fracture surface indicates high tensile loads. The fine, gray appearance of the fracture surface is consistent withStructural Steel Bolted Jointsa sudden overload instantaneous failure. Failure as a result of an overload

Bolt FailureWhen threaded fasteners are utilized, the amount of tightening or bolt torque is often important.. The appropriate torque is required in order to prevent relative flexing of the two parts being fastened and to assure an acceptable mechanical connection. Structural Steel Bolted JointsFailure from improper torque

Inspection department responsibility on capital projects is to provide the Company with an independent Quality Assurance assessment function that assures compliance with the Companys Engineering requirements, and provide specialized inspection and Non Destructive Testing Services that assures optimum economic quality is maintained throughout the life cycle of the Companys facilities to minimize losses due to unscheduled events and to maximize Company profitability. ( SAEP 1150)CONCLUSIONStructural Steel Bolted Joints

And this task can be a accomplish byCONCLUSIONStructural Steel Bolted Joints

Prepared and PresentedAkram M. MegdadBAPIUStructural Steel Bolted Joints