钢筋混凝土梁抗弯刚度公式修正及研究_英文_

MODIFICATON AND RESEARCH ON BENDING RIGIDITY

　Foundation item :Suppo rted by the Comm unication Scientific R esearch Pr oject of Jiang su P ro vince(06Y 21).　Received date :2010-03-05;revision received date :2010-04-01　E -mail :aijun 0822@nuaa .edu .cn

FORMULA OF REINFORCED CONCRETE BEAM

A i J un ,Chen J ue ,Zhang L if ang ,L iu F ang

(Colleg e of A er ospace Eng ineering,NU AA ,29Yudao Str eet,N anjing,210016,P.R.China )

Abstract :Bea m stiffness deg rades w ith its age in serv ice and its ser vice per for mance is w eakened.A cco rding to the fundamental cha racter istics o f the reinfo rced concrete,the influence of stiffness degr adat ion caused by different kinds o f damag e is obtained .A mong them ,the crack is the most dir ect and obv ious factor .Fur therm or e ,acco rding t o the analysis of bending r ig idity for mula pr esented in cur rent standa rd ,an influence paramet er of crack dev elo pm ent o n the st iffness deg ra dation,i.e.,no nunifo rmity coefficient o f tensile st eel st rain ,is ext racted.A ver age cr ack distance and cr ack depth ar e t aken as cr ack stat istic pa rameter s.Based on analy sis and mo deling with A NSY S ,t he m odified bending rig idity for mula r elated t o cr ack is o btained .Key words :reinfo r ced concrete ;beam and g ir der s;stiffness;cra ck;AN SY S

CLC number :U 446 Document code :A Article ID :1005-1120(2010)04-0299-07

INTRODUCTION

At present ,simple discounted estimatio n metho d is o ften used to char acterize br idge girder stiffness in home and abr oad standards .Such metho ds ar e valid in general bridg e design,but fo r service br idge assessment they ar e limited .With the incr easing of service ag es,cr acks and dam ag e,

such

methods

g radually

cannot

characterize the actual stiffness,and can cause unnecessar y inter ference and error to the bridg e inspection.So research o f the method that can accurately characterize actual stiffness of the bridge beam by the damage param eters is necessary.

1　INFLUENCE OF DAMAGE ON

CROSS -SECTION STIFFNESS

Reinforced concrete is composite m aterial.There are thr ee commo n damag es in use which are co ncrete cracks ,concrete corr osion and steel co rrosio n .The formation mechanisms of these dam ag es are co mplex ,diverse and differ ent ,but all o f them hav e an influence o n bending r ig idity ,

and directly o r indirectly lead to the deg radation of structur al stiffness.Amo ng them ,concrete cracks play the most direct and obvious role in stiffness deg radation .

Accor ding to the basic theory of stiffness analytic method [1]

,a form ula of beam stiffness in norm al case is

B s =

E g A g h 02

1.15 +0.2+6n

(1)

w her e E g ,A g ,h 0,n , are all inv ar iant ,and those not keep in pace with the changing o f the str ucture external fo rce.No nuniform ity coefficient of tensile steel strain is the only variable about structure external loads.T he law of specific variatio n can be given by

= 1.11-M cr

M

(2)

w her e M cr is the cracking mo ment of member ,and M the mom ent v alue o f current ex ter nal loads.

Eq .(2)show s the nonuniformity coefficient of tensile steel strain gr adually becom es larg er from zero w ith the increasing of the ex ternal load after crack.And the value of the member stiffness B s will also gradually degrade from the