New Strategy to Mitigate Earthquake Damage of Wood Houses. New Strategy to Mitigate Earthquake Damage of Wood Houses

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1 New Strategy to Mitigate Earthquake Damage of Wood Houses Kyoto Univ. Regenerative Preservation of Built Environment Department of Architecture and Architectural Engineering Yasuhiro HAYASHI New Strategy to Mitigate Earthquake Damage of Wood Houses Probability of seismic intensity greater than 6 - in the next 3 yrs OSA Any policies for the seismic retrofit promotion have not succeeded yet in almost all municipal government. KOC Probabilistic Seismic Hazard Map Strategy considering Regional seismic environment Durability of regional houses as well as seismic performance

2 Principal earthquakes occurred in the last century 9~95 95~2 Case of M>6 earthquakes EQ. in the Sea Area Shallow Inland EQ. Inland shallow EQ & EQ. In the Sea Area 995 Kobe EQ. OSA Acc (Gal) Kobe EQ. (Kobe) KOC Asp Asp 2 Asp 3 Acc (Gal) Acc (Gal) Time (s) Time (s) Time (s) (OSA) (KOC) 23X Nankai EQ. 23X Nankai EQ. (Kamae et.al)

3 Kobe (995 Kobe EQ.) (23X Nankai EQ.) Kochi Osaka Predicted ground motion intensity (Osaka Pref.) Nankai EQ. Uemachi Fault Ikoma Fault

4 995 Hyogo-ken, Kobe EQ. Over 64 people were killed. Most of them are due to the collapse of old wood houses. 2 Western Tottori Pref. EQ.

5 Influence of construction years 棟 Ashiya-city (Kobe EQ.) % 9% 8% 7% 6% 5% 4% 3% 2% % % No Slightly Half Completely Hino town (Tottori EQ.) % 9% 8% 7% 6% 5% 4% 3% 2% % % 棟 Completely destroyed Slightly Half Completely Tottori Skill of local carpenters Rich supply of high quality material

6 Influence of decay and termite attack (Kobe EQ. by Miyano et.al.(996 )) Damage level Completely Half Slightly % 9% 8% 7% 6% 5% 4% 3% 2% % % Without decay/termite attack With decay/termite attack Damage by termite attack Influence of decay/termite attack (Kobe EQ.) -'5 '5-'6 '6-'7 '7-'8 '8- All with decay/ termite attack without decay/ termite attack Ratio of completely damaged houses PGV (cm/s) If houses are not affected by decay or termite attack, variation in damage ratio with construction years is not so large damage ratio for old houses remains small as well as Tottori EQ.

7 Old houses in Osaka Outline of method for damage prediction Modeling of wooden house Estimated ground motion Modeling of wooden house Mud wall Hanging wall Column Estimation of maximum drift angle Investigation of structural properties Probability of damage Modeling of wooden houses based on the method of seismic performance evaluation.

8 Outline of method for damage prediction Estimation of maximum drift angle Estimated ground motion Modeling of wooden house R:Maximum drift angle Estimation of maximum drift angle Estimated ground motion Probability of damage Estimation of the maximum drift angle from response analysis. Outline of method for damage prediction Damage probability Estimated ground motion Estimation of maximum drift angle Modeling of wooden house Probability of damage (%) 5 Half collapse Complete collapse Probability of damage.5..5 Maximum drift angle R (rad) Fragility functions Predicting damage probability by using the fragility functions of maximum drift angle.

9 Variations of fragility function due to aged deterioration Probability of damage P f (R) P f (R, T)=Φ (( ln(r)-ln(r m (T))) /ζ R ) R m (T) = R m f (T) 5% Φ:lognormal distribution Durability is is poor good ζ R :standard variation T: years after construction Aged deterioration R m (T) f(t) R m R m (T) R m Maximum drift angle R R m,the median of the maximum drift angle, changes due to aged deterioration. Proposal of reduction function f(t) of seismic performance Median R m R m f (T) = max{exp (-α (T/( T )) 2 )} R m (T) = R m f (T) Τ : Expected lifespan R m e -a T: Years after construction T

10 Variations of reduction function f(t) by expected lifespan T.8.6 f(t).4 Τ =25 Τ =5 Τ =.2 α= T (Years after construction) The aged deterioration of wooden houses with longer expected lifespan is slower. Variations of R m based on seismic damage data Kobe-city Damage ratio (%) Hino-town all R m.2.8 Hino-town Peak ground velocity (cm/s).4 Damage ratios based on Kobe EQ. and Tottori EQ. Kobe-city Complete collapse T (Years after construction) Kobe-city: R m decreases suddenly when the years after construction exceeds 2 years. Hino-town: R m does not change a lot in general.

11 Comparisons of reduction functions f(t).8 Ηino-town Kobe-city Τ =25 f(t) α=.7 Kobe-city T (Years after construction) Hino-town Τ = The proposed reduction function f(t) could explain well variations of R m obtained from damage data in two EQs. Expected lifespan (yrs) T = 3 ( P B C D ) β Kobe T =33yrs Tottori T =8yrs Kobe Tottori Durability.5.65 Structure.8.5 Inspection.. Climate.9.5 Maintenance.27 Design manual considering durability

12 全壊確率Damage Probability Simulation Old house(built in 925) / New house(built in 985) Hihg durability Low durability Seismic performance of houses Cy=.5,.2,.4 Seismic retrofit is performed now (25). Nankai EQ./Inland EQ. will occur in 23 (25 year later). Old house New house Retrofit EQ How should old house in Osaka prepare for Nankai EQ. C y =.2 C y =.5 Nankai EQ..8.6 No retrofit P f R (rad) 最大応答変形角 We should gives priority to seismic retrofit of houses with very poor seismic performance.

13 全壊確率How should old house in Osaka prepare for Inland (Uemachi( Uemachi) ) EQ..8 C =.4 y No retrofit Low durability Inland EQ..6 P f.4.2 High durability (25).5..5 R (rad) 最大応答変形角 It is necessary to build houses with high durability as well as high seismic performance.

14 全壊確率How should new houses in Kochi prepare for Nankai EQ. P f C y =.5 No retrofit (T =25yrs) C y =.4 Low durability High durability Nankai EQ R (rad) 最大応答変形角. Maintain houses with high seismic performance. 2. Rebuild houses with high durability.

15 Conclusions To reduce the damage of wooden houses in big earthquakes to occur in the future, it is inadequate to retrofit wood houses with poor seismic performance although it is effective. The maintenance of houses by the owner and local carpenters after a retrofit is also very important to hold the high seismic performance for a long term. Strategy to prepare for the coming earthquakes should change region to region.