safety assessment

1. Q1 : explained the featureof followingseismicretrofittingmethodsof steel bridgepiers
A:Basedon conceptof seismicdesign(figure1) ,one of the importantconsiderationsontheseismic
designandretrofitof steelbridgepiersistoincrease the ductilityof existingsteel bridgepierswhile
keepingtheirultimatestrengthalmostunchanged.Inorderto retrofittingof steelbridgepiers,there
are kind of method adopted, in this report we just explain 2 kind of method that is adopted to
retrofittingsteel bridge pierssuchasfollow below.
a. Concrete fillingmethod
Partiallyfillingthe hollowsteeltube withconcrete (andtherebyusingcomposite construction)
is one of the mostsuitable available methodsforimprovingstrengthandductilitybecause the
concrete core inhibitslocal bucklingof the thinsteel tube and,atthe same time,the steel tube
provides a confining stress to the concrete core. In this method existing steel tubular columns
are retrofittedby
1. Fillingwithconcrete inside steel sectionsfromthe base,uptoan optimal level;
2. Providinginnersteeltube andfillingthe gapbetweentubes,uptoanoptimal level;
3. Placinga diaphragmoverthe filled-inconcrete.
Figure1. Concept of seismic design and retrofitting
The supremacyof thismethod:
1. fully concrete-filled steel bridge piers can substantially increase stiffness, and/or strength,
but they behave in a relatively brittle (nonductile) manner and do not provide sufficient
ductilitytoresistvery strongearthquakes( Figure 1bforthe fullyconcrete-filledcolumncurve);
2. foundationstructuressupportingbridge piersbecomelarge andexpensive ifthe self-weight
and strengthof the piersare increased.
b. Corner reinforce structure
To prevent cracks at the corner parts of the box cross section, the following 5 restrictionscan be
regulatedaccordingtothe newJSHB, PartV - SeismicDesignCode.
1. Two timesthe widthof a plate panel,hc, ina reinforcedcorner,showninFig.2, shall be taken
more than 25 % of the widthof the stiffenedplate panel,Boneach side asfollows:
2hc/B ≥ 0.25

2. where hc is the length between a corner of the box cross section and the center line of high
strengthenedboltsusedforconnectingthe cornerreinforcingplates.
2. The slenderness parameter of the corner reinforcing plate, Rc shall satisfy the following
condition.
R 𝐶 = 0,526
𝑏 𝑐
𝑡 𝑐
√
σy
E
≤ 0.4
tc E where tc isthe thicknessof the cornerreinforcingplate asshowninFig.2.
3. The geometricmomentof inertiaof the cornerreinforcingplates,Icwithrespecttothe neutral
axis of the steel box cross section shall be taken about 20 % in comparison with that of the
overall steel crosssection,lB.
4. The thicknessof the cornerreinforcingplate shall be lessthan22 mm.
5. The slendernessparameterof the cornerplatepanels,RCRshall satisfythe followingrestriction
givenbyEq. (12), whichisregulatednewlyinthisstudy.
R 𝐶𝑅 = 0,526
ℎ 𝑐
𝑡
√
σy
E
≤ 0.4
By using the cross-sectional dimensions shown in Fig. 5, the restricting conditions mentioned
above
Figure 2. Corner reinforcement (unit: mm)
Q2: Explainthe feature of deteriorationof steel bridge of yourcountry?
A: actually there were manycasescorrespondingdeteriorationof steel bridgeon mycountry,
ingeneral the failure of steel bridgeof mycountryhas similaritywiththe othercountry,
damage of abutment,crashonexpansionjoint,corrodedbearingpad,