16 sindur p mangkoesoebroto paper

7/28/2019 16 Sindur p Mangkoesoebroto Paper

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Seminar dan Pameran Haki 2010 - Perkembangan dan Kemajuan Konstruksi Indonesia 1

PADANG EARTHQUAKE OF SEPTEMBER 30, 2009WHY IT IS SO DEVASTATING

Sindur P. Mangkoesoebroto

1 INTRODUCTION

Since the remarkable Mw=9.1 earthquake hit Aceh on December 26, 2004, there havebeen frequent strong events that struck Indonesia region up to present days. One of thedevastating latest event has occurred on September 30, 2009, in the nearby Padangarea, West Sumatra. The death tolls were 383 and 48 in the cities of Padang andPadang Pariaman, and 666, 11, 81 in the regencies of Padang Pariaman, PesisirSelatan, and Agam, respectively; totaling to 1.189 deaths. The total property damage

was about US$ 500 millions due to hundred of thousands of damaged houses,thousands of collapsed buildings, roads & bridges, as well as irrigation system, widespread landslides mostly in rural areas, and other[1]; as an illustration Fig. 1 showspicture of a collapsed hotel among others. Had the earthquake accompanied by tsunamithe devastation could be much higher; however, unquestionably this was the mostdevastating earthquake that hit the region after the Acehs.

The vast destruction had caused some concerns regarding the safety of houses and

public buildings, as well as infrastructures such as bridges and embankments. However,

it should not be viewed as separate issues in a sense that the seismicity of the area that

is quite active especially recently may be an important factor; also peculiar of the last

event was its focal depth which could be categorized as deep earthquake differing fromalmost all the preceding events. This deep earthquake might have generated vertical

component which was much higher compared to the horizontal components in case of

normal events. This phenomenon could be more critical for some type of construction

materials than others. These are to add to the fact that the last event is relatively close to

the city (only about 50 km) and large in magnitude (Mw=7.6) with about VII MMI in

Padang. Dealing with the vertical component, especially for near source region, has

been stipulated in detail in most international codes; unfortunately, the Indonesia seismic

code has not sufficiently addressed the issue.

Figure 1 The collapsed Ambacang Hotel due to September 30, 2009 Padangearthquake. (Courtesy Dr. Sigit Darmawan)


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The construction material commonly used in Padang and the surrounding area for newhouses and buildings is red brick confined masonry and reinforced concrete, orcombination of the two; steel structure mostly used as rafters and to less extent can be

found in industrial buildings, and in few commercial shops. However, most traditionaldwellings used non-engineered wood structures or bamboo materials both on ground orelevated, with roof of light zinc cladding. Many houses built during Dutch era were madeof unconfined red brick masonry with considerable wall thickness (25-30 cm) and height(4-6 meters). There are many building structures that were constructed in compliance

with the national building codes, but there are also many others that apparently were not.

Among these types of constructions, the most severe damage was suffered by theunconfined red brick masonry and limitedly to the confined masonry which is normallyused in shop-houses or locally known as ruko. In well constructed structures, the framethemselves, especially of the second story and up, usually are in good or fair conditions

although the in-fill wall might undergo heavy damage or even collapse due to out-of-plane actions. Many of them suffered first story heavy damage or collapse, especially inpoorly constructed buildings, due to soft first story mechanism, or lack of anchorage orinsufficient splices or other poor detailing problems.

Prior to the last event, there had been several earthquakes shook the area, with some ofthem were relatively of high intensity (V or VI MMI) and had caused light-to-moderatedamage to various building structures. The damage, normally in the form of spalls orcracks in the structural joints or components or non-structural wall panels, usually wereleft untreated, or only treated superficially. This situation cumulatively has left lowerremaining strength of the structures to resist any up coming earthquakes. Again, albeitthis essential issue has been addressed in some countries as programs of rehabilitation,

it has not been adequately regulated in Indonesia code up to present time.

One among other important aspects to be highlighted is the instrumentation or seismicmonitoring. Although Padang is long known to belong to the area of potential highseismicity, it is acknowledged, that frequent earthquakes has been taking place only inthe past five years or so, especially after the Acehs. It is only very recently that quite afew strong motion recorders have been installed in the area. At least there are twoacceleration records available for the last event; however, one of them was not reliableas the recorder was not properly anchored to the foundation. The other machine isinstalled about 200 meters underground and the data is reported herein.

2 EARTHQUAKE ACCELERATION DATA

Two strong motion recorders were installed in the nearby area with about the samedistance from the epicenter (around 50 km). One was installed at Andalas University(UNAND) by BMKG and the other was at the underground Singkarak Hydro ElectricPower Plant (HEPP) controlled by PLN. It is unfortunate that the one at UNAND was notproperly anchored to the foundation so that it slipped during the earthquake resultingunreliable acceleration data. The data, however, was further processed and analyzed byUSGS[2]. It has given too high dynamic magnification factor for acceleration of about fourfor N-S component, while the remaining components were unavailable.

The data presented herein was acquired from the recorder installed at the undergroundSingkarak HEPP. The location of the plant, as well as the epicenter, is shown in Fig. 2.

The figure also indicates the contour of the peak surface acceleration reported by USGS.It is indicated that the peak surface acceleration in Padang was about 0.3g, and at the


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HEPP was around 0.26g which corresponds to the underground record of 0.090g (N-S),0.096g (E-W), and 0.051g (vertical) (see Fig. 3). The distance from the recorder to theepicenter is around 50 km, about the same epicentral distance of Padang. The raw

acceleration data acquired was then corrected and consistently integrated to obtain thevelocity and displacement records.

It is observable from Fig. 3, by comparing the horizontal and vertical components of the

acceleration records, the vertical component is appreciable relative to that of the

horizontal. This happens for most of the duration and, further, but for the extreme peaks,

their magnitude are about the same order. This shows the fact that vertical component

was essential in the last event; although when comparing their maximum, the vertical to

horizontal ratio is merely about 55%. Table 1 presents the extreme values for

acceleration, velocity and displacement records.

Table 1 Extreme values for acceleration, velocity and displacement of Mw=7.6, Sept. 30,

2009 Padang earthquake as recorded at the underground Singkarak HEPP.

Figure 2 The epicenter of Mw=7.6, Sept. 30, 2009. Contour of surface peak acceleration

reported by USGS, and the location of the SMA recorder in the underground Singkarak

HEPP.

3 Response and Power Spectra

As normally carried out, the response spectra are generated for the recorded groundmotions. Based on the corrected acceleration given in Fig. 3, the 5%-damped response


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spectra are constructed for three components. The results are shown in Fig. 4. Themaximum spectral values and their corresponding frequencies are presented in Table 2;and the dynamic magnification factors as defined as the ratio of the maximum spectral

with respect to the maximum record values are shown in Table 3. It is worth to note thatthe vertical dynamic magnification factors are higher than those of the horizontalcomponents. By observing the corner period of around 0.50-0.75 seconds, it can beenvisaged that the rock formation around the recording site is not of the compact rocktype as normally indicated by Tc=0.4 seconds for rock[3].

Table 2 Maximum spectral values (=5%) and their corresponding frequencies.

Table 3 Dynamic magnification factors for acceleration, velocity, displacement, andpower.

The excitation power is defined as the energy per unit time supplied to the simple

oscillator by the ground excitation, which is equal to the product of the inertial force andthe ground velocity; and the absorbed power is the energy per unit time absorbed by the

simple oscillator through the dashpot and the spring, equals the sum of the damping and

the spring forces multiplied by their relative velocity. Mathematically, the excitation and

the absorbed power densities (power per unit mass) are expressed as follows[4],

The excitation and the absorbed power density spectra are shown in Fig. 5 for three

components; and their magnification factors are indicated in Table 3. It is observable

from the figure that the E-W component is the most powerful, and the vertical is the

weakest, being only slightly less than that of N-S component. Note that the power densityhas unit of horse power per ton mass.


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Figure 3 Corrected acceleration records (as), and their corresponding velocity and displacement (v and ds) time series for N-S, E-W,

and vertical components. Shown also are their extreme values. Raw acceleration data was recorded at the underground Singkarak

HEPP.


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Figure 4 Response spectra of the corrected acceleration records, =5%.


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4 GROUND MOTION ANALYSIS OF PADANG AND ITS VICINITY

As mentioned earlier, reliable acceleration ground surface record for Padangearthquake of September 30, 2009, is unavailable; therefore, some combination ofinformation obtained from several sources will be carried out to perform further analysis.USGS has developed a contour map for the peak surface acceleration and is presentedin Fig. 2. City of Padang is located around 50 km from the epicenter, about the sameepicentral distance of the recording machine at Singkarak HEPP. The peak accelerationestimate for Padang is 0.3g and that for Singkarak HEPP is 0.26g at surface. This peaksurface acceleration is closely dependent on the soil condition of the region in question.The geological information for Padang is alluvium deposit[5], in general, and can beclassified as medium soil. Based on this information the required peak groundacceleration specified by Indonesia seismic code for Padang area[3] is 0.33g. Moreprecisely, for the area the code specifies the peak ground acceleration of 0.25g for

bedrock, 0.29g for hard, 0.33g for medium, and 0.36g for soft soils.

As described earlier the acceleration data recorded at Singkarak HEPP was obtained atelevation of about 200 meters below the ground surface. The characteristic of therecorded acceleration may differ from that at the surface, however, it will be maintainedand the maximum acceleration is scaled to that of the USGS value for Padang, i.e., 0.3g.More over the ratio of the vertical to horizontal peak ground acceleration is taken to be70% as suggested by the code. A modified acceleration spectra are then generatedaccording to the previously mentioned procedure and compared to that of the code. Thecurves are shown in Fig. 6 for horizontal (top) and vertical (bottom) components.Similarly, vertical code acceleration spectrum is taken as 70% that of the horizontal.

Fig. 6 (top) shows that the horizontal acceleration spectra are lower than that of the codeexcept for periods of about 1.4-1.6 seconds where the E-W spectral values are almostthe same as that of the code. This, however, is not the case for verticalcomponent (bottom). In general, the spectral values of the vertical components are veryclose to that of the code for wide range of periods. The reason for this is that becausethe acceleration dynamic amplification factor is higher for vertical component (2.75) ascompared to that of the horizontal (2.2 on average). This has raised the concern ofcoping with vertical component in seismic resistant structural design, especially the issueis about the sufficiency of taking the vertical component as 70% to that of the horizontalfor some seismically critical regions.

The excitation and absorbed power density spectra as shown in Fig. 7 for threecomponents can better illustrate the significance of the vertical component. In general,the absorbed power is appreciably higher than the excitation at period range of 0.5-2seconds for all three components. The highest absorbed power demand is for the E-Wcomponent of 2.65 hp/ton, followed by the vertical of 2.2 hp/ton, and the least in N-Sdirection of 1.9 hp/ton. It can be seen that on average the absorbed power demand inhorizontal direction is of the same magnitude of that of the vertical. Further more, acloser observation reveals that the absorbed power consistently higher than that of theexcitation in the period of interest for vertical component; it is in contrary to that of thehorizontal. This might explain the critical role of vertical component in case of Padang,September 30, 2009 earthquake.


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Figure 6 Modified response spectra of Padang earthquake, September 30, 2009,compared to that of the code. Top for horizontal; bottom for vertical components. =5%.

Figure 7 Modified power spectra of Padang earthquake, September30, 2009, for three components, in horse power per ton mass. =5%.


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5 SOME EXPERIMENTAL RESULTS

Experimental investigations have been carried out for some structural specimens andmaterials[6,7,8,9]. Full-scale beam-column sub-assemblage models of steel as wellas concrete have been tested under cyclic displacement history. Another experimentwas performed on full-scale confined masonry panel also in cyclic manner. Some ofthe results which is relevant to be discussed herein, i.e., the hysteretic energy capacityper cycle versus the drift ratio, is presented.

The typical model of the confined masonry investigated is shown in Fig. 8 (left). Therewere totally six specimens which were divided into two groups. Two types of materialinvolved are red brick and lower-quality concrete block or locally known as conblock.Group 1 investigates one red brick panel and two conblock specimens. One conblockspecimen is an ordinary panel, while the other has horizontal reinforcement at every

mortar joint running from the end-to-end confining non-structural columns. The over alldimensions of all specimens in Group 1 are 1,070 x 1,330 mm2 (including two end-confining non-structural columns of 100 x 100 x 1,330 mm3 reinforced by 4 D-10 rebar);panel thickness is 100 mm. Group 2 performed similar experiment for three specimensall made of red brick with different configuration of the intermediate confiningnon- structural columns or beam. The specimen dimensions are 2,200 x 2,100 mm(including two end-confining non-structural columns of 100 x 100 x 2,100 mm3 with 4 D-10 rebar); panel thickness is 100 mm. Unlike the first, the second specimen hasvertical non- structural column inserted in the middle between the end non-structuralcolumns; and the third has non-structural beam inserted in the mid-height of the secondone. Vertical load resulting 0.4 MPa compressive stress was applied during theexperiment to all six specimens. The typical resulting hysteretic loops are shown in Fig.8 (right). Based on the hysteretic loop, a relationship between hysteretic energycapacities per cycle versus drift ratio can be constructed.

By looking at the hysteretic loops it can be observed the phenomena of stiffnessdecrement and pinching, which become more appreciable at higher cycles. Physically itcorresponds to crack formation and the widening of the crack gaps. Therefore it can bereasoned that the reduction of the hysteretic energy capacity is related to the numberand to the width of cracks in the energy dissipating sections.

Figure 8 Crack pattern and typical confined masonry specimen (left),the resulting hysteretic loops (right).

Another experiment was performed on two concrete beam-column sub-assemblies;


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see Fig. 9 (left). One assembly was conventionally detailed as required by code for fullyductile section especially for its beam segment close to the column, and also satisfyingthe strong column weak beam criteria. A beam stub on the other side of the column was

facilitated to ensure no-rebar-slip on the critical column face of the beam. The otherspecimen was similar to the first, however, pairs of diagonal web rebar was added toimprove its shear strength and to control the crack distribution in hoping of enhancementof the energy dissipating capacity. The detailed is shown in Fig. 9 (left) with dimensionsin mm, and the resulting hysteretic loops are in the right. It turns out that the additionaldiagonal web rebar has increased the energy dissipating capacity, and reducing thepinching phenomenon that is commonly associated with conventionally shear-reinforcedconcrete section.

The observation of the hysteretic loops reveals that minor pinching phenomenon hasbeen noted, however, the stiffness decrement remains noticeable. Visual observation

during the experimental run shows cracks with thin gaps but well distributed in relativelywide area. The other specimen without diagonal rebar (not shown) present higherpinching but with the same stiffness decrement, and this corresponds to moreconcentrated cracks in narrower area with larger gaps.

Figure 9 Typical concrete beam column sub-assembly (left, dimensions are in mm), andthe resulting hysteretic loops (right) for the energy dissipating beam section.

Experiment was also performed on a steel beam-column sub-assembly. The specimen

was of compact section so as to satisfy requirements of fully ductile section and strong

column weak beam. The specimen is shown in Fig. 10 (left) with dimensions in mm, and

the resulting hysteretic loops are in the right. The pinching is not observable in this

experiment, but the stiffness decrement due to local buckling, especially in the web, was

noticeable.


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Figure 10 Steel beam column sub-assembly (left, dimensions are in mm), and theresulting hysteretic loops (right) for the dissipating beam section.

Based on the experiments, relations of hysteretic energy capacity per cycle versus driftratio is constructed and shown in Fig. 11. From the figure it can be learned about therobustness of steel structure and the inferiority of confined masonry, while concretestructure is in between them. The steel specimen can undergo a drift ratio as high as3.5%, or ductility value of almost 5, with the energy capacity about twice that of theconcrete at approximately the same drift ratio. Concrete can achieve drift ratio as far as

4.5%, or ductility value close to 5, with higher energy capacity for one with diagonal rebarthan that with none. Confined masonry can sway for as high as 1.5% inter-story drift ratiowith very low energy capacity. The achievable drift ratio should be compared with thelimiting values from the codes[10, 11], e.g., 0.7-1.3% for masonry buildings, and 2-2.5%for any other structures. The drift limitation of 2-2.5% for concrete and steel structureimplies the ductility value of about 2.5-3 for steel and 2-2.5 for concrete which are muchlower than the maximum experimental values of 4 and 5 for steel and concrete,respectively. This means there is ample safety margin for the typical steel and reinforcedconcrete components to be used in seismic regions as long as proper detailing isprovided.

When used as infill wall or panel, the confined or unconfined masonry is limited to much

less drift ratio of 0.7-1.3% than that of the framing concrete or steel structures. This

emphasizes the need of seismic gap between the panel and the enclosing frame, which

is, unfortunately, commonly disregarded by builders in Indonesia, even in moderate

to high seismic zones. Considering these common practices and also its low energy

capacity, the failure of confined masonry has occurred rather early during the

earthquake, and frequently fall down due to out-of-plane forces.


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Figure 11 Hysteretic energy capacity per cycle versus drift ratio for confined masonrypanel, concrete, and steel beam-column sub-assemblies.

6 CUMULATIVE DAMAGE

The important effect of earthquake duration has been discussed in some researchreports and can be found elsewhere[4]. In Ref. [4] the duration is categorized as short,moderate, and long. The effect of duration enters into the picture through the hystereticenergy spectra of the models being investigated. For the kinematic hardening model, for

instance, the mean hysteretic energy demand for long duration is about 1.4 that ofmoderate, and about twice that of the short durations. In experimental run the hystereticenergy is associated with deterioration in the form of cracks, yielding, plastic hingeformation or local buckling, during the post-elastic regime. More deterioration will occurwhen more post-elastic displacement cycles is imposed, whether continuously orintermittently. This phenomenon should be closely observed in case of Padangs lastearthquake, because prior to this last event there were several strong earthquakesstruck the region.

Table 4 lists some major earthquakes that shook the region during 2005-2009. There areat least five earthquakes occurrences before the most devastating one in September30, 2009. The earthquake intensity ranges from IV-VII MMI, and the depth varies from

shallow to normal except the last one that belongs to deep earthquake. Considering theratio between the depth to epicentral distance, it can be expected that the verticalcomponent is the most significant in the last event.

The largest magnitude occurred in 2007 with VI MMI and its epicenter was about 185 kmfrom Padang. The event had caused light to moderate damage to so many buildingstructures, mostly concrete, as well as infrastructures; similar situation was also the caseof the April 2005 event although with lower scale. Despite the structural damageincurred, most structures that survive those events were left untreated for cracks orspallings in their critical sections, unless for some non-structural or cosmetic repair.


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Table 4 List of Some Major Earthquakes Occurred Around Padang between 2005 -2009 (USGS)

The cracks formed in concrete or masonry structures during the earthquake havereduced the hysteretic energy capacity of the structural components. On the other hand,it is not very easy to fill the gap by injecting epoxy or cement-based material intostructural building joints. Even if this injection were performed, it was hard to inspect andto test to verify the results. Moreover it is unclear how the structure would behave in thenext earthquake event, and therefore doubting the benefit over cost of the treatment.Certainly, the structures that left untreated for the cracks will have lower energy capacitythan they were before the event. Due to some major earthquakes prior to the last one,

much cumulative damage has occurred and further reducing the energy capacity of therelevant seismic resisting components. This condition has, presumably among otherimportant factors, caused the extensive destruction in case of September 30, 2009Padang earthquake. Despite this important issue, the Indonesia code has not regulatedon how to deal with it.

7 DISCUSSIONS AND CONCLUSIONS

Several aspects have been presented and highlighted regarding the presumably keyissues in relation to the September 10, 2009 Padang earthquake; especially consideringits vast destruction. These include common local construction practices, the property ofthe construction materials used, the regional seismicity, the characteristic of the

earthquake, and the national building structure regulations. Other important issues, butuntouched in the paper, that should be dealt with is raising the public awareness as wellas mitigation in case of natural disaster, especially earthquake, for the area or regionwith high risk. The discussion of the latter can be found in Ref. [2].

Observing at the local culture and in the vicinity of Padang as well as the geologicalformation of the region, it must be clear that local people are aware of their condition asbeing prone to earth movement. Traditional dwellings and all kind of buildings that areconstructed from wooden structures with light roof can be found almost every where inthe region. However, due to seismic silent for long period that has the effect of loweringawareness, and better economic growth, authorities and public in general startconstructing relatively modern structures for offices, houses, and other buildings. Some

of them well comply with the national building code and some otherwise, while the localenforcements of the regulations were not ready for the boom and tend to be weak.


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The lesson learned from the last event is that the public and authorities shouldreconsider all procedures to build safe constructions, to increase the public awareness ofthe natural threats that always in wait, to exercise the mitigation plans, to perform the

post-earthquake assessment and rehabilitations, to review and up date the buildingcodes, and to critically asses the deficiency of the systems or regulations in place. Thelatter emphasizes that strong earthquake such as the last one may not necessarily meanthat the required level of horizontal design earthquake should be increased as there is nosupporting evidence based on the earthquakes that occurred thus far. However, there isneed to observe the proper selection of construction materials, to deal with the verticalcomponent of earthquake, and to account for the cumulative damage, besidesimprovement of the commonly technical procedure such as seismic resistant design andsectional detailing. These aspects should be formally specified in the national buildingcode and strictly adopted and enforced during the designs and constructions.

In conclusion, based on the presentation outlined earlier the key issues that should behighlighted are as follows:

a) The vertical component of the last earthquake plays significant role as were notclearly observed in almost all former events. Therefore, the code should betterregulate the vertical component of earthquake both in design procedures and torevise its present fractions.

b) The low remaining strength of the critical structural components due to the previousearthquakes, which were left untreated, has caused inadequate energy dissipatingcapacity of structures in coping with the last event. In the future, there shall beeffective regulations for post-earthquake assessments and rehabilitations ofstructures and shall be required in the code.

c) The severe damage that suffered by most masonry brick wall constructions, notablefor their relatively low strength compared to concrete or steel materials, shows itsunsuitability for region of moderate to high seismicity. Consequently, there should bestringent rules regarding the selection of construction materials used, and more ondesign procedures such as the determination of structures ductility level andsectional detailing, especially, for the first story of multi-story building structures.

d) Based on the earthquakes that have occurred thus far, there is yet no evidence toincrease the required level of horizontal design earthquake in Padang and its vicinity,as the problem more related to the vertical component of the ground motions, orothers.

e) Due to the limited reliable earthquake data, more monitoring instruments, e.g., strongmotion recorders, should be installed in the region so that better earthquake analysiscan be performed in the future.

8 ACKNOWLEDGMENT

The author acknowledges Mrs. Netto Mulyanto, Riza N. Gustam and Andrianto, of PT

PLN (Persero) for the earthquake data provided and reported in the paper.

REFERENCES

Pikiran Rakyat, Kerugian Gempa Sumbar Rp. 4,8 Trilyun, Kamis, 29 Oktober, 2009.

--------, Learning from Earthquakes: The Mw 7.6 Western Sumatra Earthquake of


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September 30, 2009, EERI Special Earthquake Report, December,2009. [http://www.eeri.org/site/images.PDF]

SNI 03-1726-2003, Provision for Seismic Resistant Structural Building Design, IndonesiaNational Standard, 2003. (Document in Bahasa.)

Mangkoesoebroto, S.P., Seismic Performance Chart for Simple Structures,Indonesia Centre for Earthquake Engineering, Research Report SeriesNumber 1/2007 (ISBN 978-979-16472-0-5),August, 2007. [http://www.icfee.info]

Kastowo, D. and Gerhard, W.L., Geology Map of the Padang Quadrangle,Sumatra, Geological Survey of Indonesia, Geology Quadrangle Map,Sumatra, Padang 4/VIII, 1973.

Mangkoesoebroto, S.P., Tambunan, S., and Goto, T., Experimental and Numerical Studyof Confined Masonry Wall Under Cyclic Loading, Journal Indonesian Societyof Civil and Structural Engineers (HAKI), Vol. 4 No. 1, May 2003.

Mangkoesoebroto, S.P., Goto, T., and Khadavi, Investigation of Full-ScaleConfined Masonry in Reversed Cyclic, The Ninth East Asia-Pacific Conference onStructural Engineering and Construction, Bali-Indonesia, Dec. 2003.

Mangkoesoebroto, S.P., Surahman, A., Batubara, S., and Irawan, P., Investigation ofFull-Scale Concrete Beam-Column Sub-Assemblies, The Ninth East Asia-Pacific Conference on Structural Engineering and Construction, Bali-Indonesia,Dec. 2003.

Mangkoesoebroto, S.P. and Sofyan, Non-Conventional Performance-BasedSeismic Engineering Applied To Strong Column-Fully Ductile Weak Beam SteelFramed Structures: Energy Perspective, Indonesian Society of Civil and StructuralEngineers (HAKI) Conference on the Excellence in Construction, Jakarta, August,2004.

FEMA 368, NEHRP Recommended Provisions for Seismic Regulations for NewBuildings and Other Structures, Part 1: Provisions, 2001.

--------, International Building Code, 2000.

Makalah ini d isampaikan dalam rangka diseminasi info rmasi melalui Seminar HAKI.

Is i makalah sepenuhny a merupakan tanggun g jawab penul is, dan t idak mewaki l i pendapat HAKI.

16 sindur p mangkoesoebroto paper

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