Mi Hn - Nhng vn lin quanL dn CTB, nhng kin thc v Hn li khng c ch trng o to trong qu trnh hc trng.Tuy nhin i lm th rt nhiu file tnh v bn v lin quan ti mi hn, nhiu khi rt xon, nay tm c ti liu ny - chia s cng vi AE l tn k s, sinh vin c bit khi nim v mi hn cng nh cc bc cn thit thit k mt ng hnHNHn l phng php ph bin lin kt kt cu thp. C rt nhiu cc tiu chun v hn, trong AWS (American Welding Society) v BSEN (British Standard European Norm) l thng dng nht.I.K HIU MI HNBng tra k hiu mi hn theo AWS A2.4 1998 (BNG 18)II.QUY CCH MI HN1. Quy cch mp hnBng tra quy cch mp hn theo AWS D1.1 2002 (BNG 19)Hnh 1:

Kch thc mi hn gcKch thc mi hn gc theo AWSTheo T-AWS D1.1 Structural Welding Code-Steel 2002, kch thc mi hn gc ti thiuc quy nh ti bng 5.8: Minimum Fillet Weld Size trang 235 nh sauHnh 2:

Bng chn nhanh chiu cao mi hn gc:Hnh 3:

Hnh 4:

III.CHN LOI QUE HNVic chn que hn cn cn c vo phng php hn, vt liu cn hn v tiu chun, quy cch mi hn.Bng tra que hn (BNG 20)

IV.QUY TRNH HNPOS ban hnh nhiu quy trnh hn. T cc quy trnh hn ny c th tra c cc thng s vt mp, khe h mi hn, loi que hn, ng knh que hn cng qu trnh gia nhit ng vi vt liu cn hn.Bng tra quy trnh hn POS (BNG 21)V.TNH MI HN1. bn ca mi hnTheo ASD, bn ca mi hn c ly theo ng sut cho php. ng sut tnh ton ca mi hn khng vt qu ng sut cho php ca mi hn.

Theo LRFD, bn ca mi hn ly theo bn thit k ca vt liu cn hn (base material, FBM) hoc bn thit k ca vt liu lm que hn (weld electrode, Fv), ly gi tr no nh hn. bn ca mi hn phi ln hn bn yu cu tnh bng cch phn chia ti trng truyn qua din tch hu hiu ca mi hn.Cc gi tr ng sut cho php theo ASD v bn thit k theo LRFD c cho trong bng3.18 - Strength of Weld ca ti liu Structural Engineering Handbook (trang 300) nh di y:Hnh 5:

2. Din tch hu hiu ca mi hn(Effective Area of Welds)Din tch hu hiu ca mi hn l din tch truyn lc lin kt tc din tch chu ti trng ca mi hn, c tnh bng chiu di tnh ton ca ng hn nhn vi chiu dy hu hiu ca mi hn.Chiu di tnh ton ca ng hn bng chiu di thc (chiu di hnh hc) tr i hai ln chiu dy hu hiu hoc bng chiu di thc nu hai u ca ng hn ko di qu gii hn ni (ng hn c bn lt hai u).2.1 Chiu dy hu hiu(Effective Throat Thickness)ca mi hn i u

STTMi hn i uChiu dy hu hiu ca mi hn

1Hn ngu hon tonLy bng chiu dy ca tm mng hn

2Hn ngu khng hon ton, vt gc kiu X, V, U, J vi gc vt ln hn hoc bng 60oLy bng chiu su vt mp

3i u, ngu khng hon ton, vt gc kiuX, V, vi gc vt t 45o n nh hn 60oLy bng chiu su vt mp tr cho 1/8 in (3.125mm)

4i u, ngu khng hon ton, vt gc kiu ch X loe5R/16 (R l bn knh loe)

5i u, ngu khng hon ton, vt gc kiu ch V loeR/2 hoc 3R/8 cho hn GMAW vi R 1in (R l bn knh loe)

Chiu dy hu hiu(Effective Throat Thickness)ca mi hn i u c th ly theo bng3.19 ca ti liu Structural Engineering Handbook (trang 302) nh di yHnh 6:

2.1 Chiu dy hu hiu ca mi hn gcChiu dy hu hiu ca mi hn gc c cc chn bng nhau c tnh bng 0.707 nhn vi chiu di chn mi hn. Chiu di chn mi hn gc c ly theo bng 3.20 ca ti liu Structural Engineering Handbook (trang 302) nh di y:Hnh 7:

J.NH MC VT T PHCc vt t ph dng trong gia cng ch to kt cu thp bao gm nhng khng gii hn cc chng loi vt t sau:- Que hn- Oxygene- Acetylene- mi- ct- G- Du bi trn, du chy my- Gng tay, mt n hn, knh hn, giVic d tr, c lng vt t ph cn s dng trong gia cng ch to kt cu thp cn c vo nh mc kinh t - k thut ban hnh ni b ca POS hoc tham kho theo nh mc gia cng v sn xut kt cu kim loi ca B Xy dng s 1776 BXD-VP phn B.