Chap3steel.korea.ac.kr/UpLoad/note/0501/7장 강의노트/강... · Web view= 70% OF TENS . STRENGTH = PROOF LOAD FOR A325 = 85~90% PROOF LOAD FOR A490 TURN-OF THE-NUT METHOD CALIBRATED

Steel DesignII Page : Connection - 1 Tel.(02) 3290-3317 Fax. (02) 921-5166 Prof. Kang,YoungJong Date :2005/ /

Chap. 7 Structural FastenersChap. 7 Structural Fasteners.

types of Mechanical Fasteners1. Rivets. Obsolete2. Unfinished Bolts,A307Lightly Loaded Member,

Cheap3. H. S. Bolts, A325, A490


4. Ribbed Bolts ( Interference Body Bolts )

- with Longitudinal Ribs,

- with Longitudinal Ribs and Serrations around

shank.


H. S. Bolts In Korea. – KS B1010

F10T

F8T


Basic Assumptions

1. No Misalignment, Pe is neglected on Ultimate

Strength.

2. No Bolt – Plate Clearence

3. Equal. Distribution of forces to each fastener.

4. Bending of Bolts Ignored.

Details of H. S. Bolts


INSTALLATION PROCEDURES

1. BEARING TYPE CONNECTION – NO PRETENSIONING

--- TIGHT “ SNUG-TIGHT”

SNUG TIGHT – Results of 1) a few impact of an impact

wrench or 2) the full effort of a man using an ordinary spud

wrench.

2. SLIP-CRITICAL CONNECTION – FULL

PRETENSIONING

PROOF LOAD

= {0.785 + ( – ) }

= A) 0.5% EXTENSION METHOD.

B) 0.2 % OFFSET METHOD.

PROOF LOAD STRESS { 70% OF TENS. STRENGTH

(A325) OR 80% OF TENS. STRENGTH (A490) }

MINIMUM BOLT TENSION

= 70% OF TENS . STRENGTH

= PROOF LOAD FOR A325

= 85~90% PROOF LOAD FOR A490

a) TURN-OF THE-NUT METHOD

b) CALIBRATED WRENCH TIGHTENING

c) ALTERNATIVE DESIGN BOLTS.-


TWIST-OFF TYPE, YIELDING TYPE

d) DIRECT TENSION INDICATOR TIGHTENING

HARDENED WASHER WITH PROTRUSIONS.


TYPICAL BOLTED CONNECTIONS.

SHEAR CONNECTION , TENSION CONNECTION

Depending on types of load transfer

1) BEARING TYPE CONNECTION.-- failure limit state.

Should meet

A) TENSION STENGTH,

B) SHEAR STRENGTH,

C) BEARING STRENGTH


2) SLIP-CRITICAL CONNECTION - serviceability limit

state

In addition to A), B) and C), should meet 2) SLIP-

CRITICAL REQUIREMENT.

LOAD TRANSFER IN BEARING TYPE CONNEC.

LOAD TRANSFER IN SLIP-CRITICAL TYPE CONNEC.


FAILURE MODES OF BOLTED CONNECTIONS.


NOMINAL STRENGTH OF FASTENERS.

A) TENSION STENGTH

cf) In 도로교시방서 허용응력설계법 - N=0.85 For F8T - N=0.75 For F10T

where

=120ksi for A325 cf) A36: =36ksi, =58ksi =150ksi for A490 A572, G50: =50ksi, =65ksi

B) SHEAR STRENGTH1) Thread Excluded

Using

2) Thread included Take 25% Reduction in Area (i.e A =0.75 )


C) BEARING STENGTH


A. Strength Limit State

L ; edge(end) distance

1-1, 2-2 actual failure line but for conservative design, assume

0

BEARING STENGTH(cont’d)

* 3rd Ed

2t L (0.6 )=1.2 L t

* Cf) 2nd Ed

; Shear strength of plate =0.62 ; tensile strength d ; bolt diameter

=


=1.24 t

Assuming that 1.24

Excessive hole deformation limit state

(upper limit)



OTHER DESIGN DETAILS.

1) MIN. SPACING OF BOLTS.For intermediate bolts, =( s-d/2 )

(S-d/2) → correspondent to where, P= factored load acting on one bolt d= diam. of bolt

LRFD-J3.3 states that s=3.0d preferably, and s

2) MIN. EDGE DISTANCE IN THE DIRECTION OF FORCE

LRFD-J3.4 states that

larger of ( , value in table J3.4)


3) MAX. EDGE. DISTANCE (J.3.5)

Le 12t 6 in.

To prevent corrosion resulting from moisture entering joints.

To ensure enough clamping action.


4) MAX. SPACING OF CONNECTORS

A) For painted members or unpainted members not subject to

corrosion.

s 24t 12 in.

B) For unpainted members of weathering steel subject to

atmospheric corrosion.

s 14t 7 in.



Shear Strength


Common Bolts vs High Strength Bolts

1) Common Bolts (A307)

- But currently not very common.

-





2) High Strength Bolts (A325, A490)- thread included in a plane of shear → ex) A325N thread excluded in a plane of shear → ex) A325X-





SLIP-CRITICAL Req’t @ Service Load.

(LRFD A-J3.8b)Slip Limit State : Serviceability Requirement.

: Thus, same as ASD.

- Pretension Load ( Tb ) = 70 % of Tensile Strength of Bolts

- Tb = friction force for each shear plane = FvAb where Fv = Nominal slip shear resistance ( Table 4.9.1)

= Slip coeff ( 0.2 – 0.6 depending on surface cond.)

- Design Slip Resistance of a Bolt in a single shear plane= FvAb

where = 1.0 for standard, oversized, shorted-slotted and long

slotted holes when the long slot is perpendicular to the line of force. = 0.85 for long slotted holes when the long slot is parallel to the line of force.


SLIP-CRITICAL Req’t @ Factored Load.

(LRFD J3.8a)

















Chap3steel.korea.ac.kr/UpLoad/note/0501/7장 강의노트/강... · Web view= 70% OF TENS . STRENGTH = PROOF LOAD FOR A325 = 85~90% PROOF LOAD FOR A490 TURN-OF THE-NUT METHOD CALIBRATED

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