THE EFFECTS OF EARTHQUAKE AND TSUNAMI LOADINGS ON STRUCTURAL BEHAVIOR OF REINFORCED CONCRETE BUILDING

This study aimed to evaluate the performance of structures such as drift ratios and internal forces arising on structural components due to earthquake and tsunami loads. The structures were modeled in three dimensions with varying heights of 3, 5, and 7-story according to the allowable building height in Bali, Indonesia. The earthquake load was designed in accordance with Indonesian standard SNI-1726-2012 and Tsunami loading refers to FEMA P646-2012. Three different loads were applied namely earthquake load, combined tsunami load 1 (T1), and combined tsunami load 2 (T2). The results showed that the drift ratios of the 3-story building structure subjected to all loads meets the criteria for a building with risk category IV, should less than 1%. However, for the 5 and 7-story building structures, the drift ratio on the first floor was only due to the earthquake load fulfilled (<1%). The drift ratio of 1.44% and 2.13% respectively were due to the loads T1 and T2 for 5-story and 2.88% and 4.67% for the 7-story building. These results indicated that the 5-story and 7-story building structure is unable to withstand the lateral forces due to the tsunami load neither load T1 nor T2.


INTRODUCTION
Most of the development and settlement patterns in Indonesia are in coastal areas [1,2] thus the buildings in these areas are not only prone to earthquake disasters but also disasters that are likely to occur immediately after a large magnitude earthquake namely the tsunami disaster. The southern coastline of Indonesia is an area that has a high level of tsunami hazard [3][4][5][6]. During the Indian Ocean tsunami struck Aceh area on December 26 th , 2004, a large number of reinforced concrete structures both designed and not following the building code suffered partial or total collapse [7,8]. Low-rise wooden frame buildings and unreinforced brick buildings suffer heavy damage due to hydrodynamic pressures generated by the tsunami and collision forces by debris carried by the tsunami waves [9]. To minimize casualties during a tsunami, a strategy for disaster mitigation is needed [10,11]. According to FEMA P646 in 2012, most of the tsunami mitigation efforts carried out were vertical evacuations to higher levels of specially designed building structures with construction that could withstand earthquake and tsunami loads [3]. Therefore, this study was conducted to be able to evaluate the effect of earthquake and tsunami loads on the behavior of reinforced concrete structures. The aim is to evaluate the level of resilience of a structure designed to withstand earthquake and tsunami loads [7].

EARTHQUAKE LOAD ANALYSIS
The earthquake load calculation in this study uses an equivalent static lateral force analysis according to Indonesian Earthquake Code (SNI 1726:2012) and [12]. This is because the hotel building planning is a building with a structure that tends to be square, regular and symmetrical. The steps undertaken to determine the earthquake loads based on an analysis of equivalent lateral static force are as follows:

Building risk analysis
In this stage, the steps that must be taken are determining the type and function of the structure to be built and determining the risk categories based on Table 1 of the Indonesian National Standard on Earthquakes, and determining the importance seismic factors (I e ) based on risk category obtained previously.

Regional response spectra
The followings steps are taken to form the regional response spectra: 1. Determination of the spectral response acceleration at short periods (Ss) and the spectral response acceleration at 1-second period (S1). Table 3 of SNI-1726-2012 are determined based on the type of soil at the building site [6]. 3. Determination of site coefficients (Fa and Fv) in Table 4 and Table 5 of SNI-1726-2012 [3]. 4. Determination of maximum spectral response parameters (SMS and SM1) [6].

The site classifications listed in
(1)

Equivalent static analysis
The stages of equivalent static analysis are as follows [6]. 1. Fundamental period of structure (Ta) obtained by Equation 3.
2. Determination of the response modification coefficient (R). 3. The seismic response coefficient (Cs) is determined based on Equation 4.
4. The seismic base shear force (V) in the specified direction must be determined in accordance with Equation 5.
5. Determination of lateral force between levels. In the equivalent static analysis, earthquake forces that hit the base of the building will be distributed at each floor / building level according to Equation 6.

TSUNAMI LOAD ANALYSIS
The tsunami load to be planned on a building structure must take into account the following loads: hydrostatic force, buoyant force, hydrodynamic force, impulsive force, impact force, the force due to water containment from water-borne debris, uplift force on the floor [13,14].

Hydrodynamic force (Fd)
Hydrodynamic loads on building structures are applied when there is water flow around the structure or components of the building structure. Hydrodynamic load is a function of flowing fluid density, flow velocity, and structural geometry. Based on FEMA P646 [3], the hydrodynamic force can be calculated using Equation 7. (7)

Impulsive force (Fs)
Impulsive force is the force caused by the foremost wave of water that hits a structure so that it puts a heavy impact on the structure. Based on FEMA P646 [3], to get a conservative value, it is recommended that the value of the impulsive force be 1.5 times the hydrodynamic force as written in Equation 8.

Impact force (Fi)
The impact force from debris carried by water (such as tree trunks, pieces of wood, ships, containers, vehicles, buildings) can be a major cause of building damage. The impact force of debris can be estimated using Equation 9 [3].

Debris damming loads (Fdm)
Damage caused by the accumulation of debris carried by water can produce a force that comes from the water that carries it. The value of this force is determined by the extent of the debris that damages the surface of the structure. The magnitude of this containment effect is calculated by referring to the equation used when calculating the magnitude of the hydrodynamic force, can be seen in equation 10 [3].

Lifting force on the floor (Uplift)
Lift force will work on the floor of a building submerged by a tsunami inundation. The hydrodynamic force can also work vertically on the floor plate. As long as the water flows quickly, rising water can lift the bottom (soffit) of the horizontal component of the structure, adding to the buoyancy upward estimated by Equation 11 [3].

COMBINATION OF TSUNAMI FORCES
From the combination of tsunami forces on the overall structure, the combination of tsunami loads for building structures is as follows [3].

RESEARCH METHODS
This research uses numerical modeling methods with SAP2000 software. The steps taken in this study are as follows.
1. The initial stage of this research is to make a structure model of buildings 3, 5, and 7 floors in accordance with the planned floor plan itself according to the estimation of the researcher. 2. Evaluation for earthquake loads as seen from the comparison between static earthquake loads and dynamic earthquake loads and the results of drift between building floors that have met the requirements before the structure is loaded with tsunami loads at a later stage. 3. Analysis of tsunami loads with the calculation of tsunami forces and combination of loading refers to FEMA P646 of 2012 which is then evaluated on the results of structural analysis with tsunami loads. Then compare how the effect of earthquake and tsunami loads on the behavior of building structures as seen from the internal forces, drift, and drift ratios that occur. The results of the comparison will be presented in data tables and graphs [3,15]. 4. From the results of the analysis, conclusions and suggestions are made.

Data collection
In this planning the data is collected using primary data. Primary data obtained are assumptions and estimates from researchers, such as; structure plans, structural geometry data and loads that will work on buildings.

Data of structures
The planned structure is the structure of a reinforced concrete moment frame building that is designed with a special moment resisting frame system with the function of a hotel which is also a monumental building located in the Banda Aceh City Center area with class E site on a soft ground location. Building structures with varying heights are buildings 3, 5 and 7 floors with typical floor plans. Typical structure plans for variations in floor height can be seen in Figure 1.

Data of material
The type of material that will be used in building structure planning is reinforced concrete material, with the following data:

Structural geometry data
The building structure made is a frame system of reinforced concrete moment frames, with initial geometry data for structural modeling for each type of building structure as follows:

Earthquake load calculation
Based on calculations that have been carried out on building risk analysis, formation of regional spectral responses and equivalent static analysis, the calculation of lateral force between floors using Equation 6, the magnitude of lateral forces at each floor is presented in the following Table 2.

Evaluation of dynamic earthquake load analysis
To meet all the performance criteria of building structures against earthquake loads it is necessary to compare the results of the analysis of static earthquake loads with dynamic earthquake loads. In the analysis of dynamic loads using parameters that have been calculated in the formation of response spectra design is then analyzed in the SAP2000 program using the response spectrum analysis method. Thus, comparative data obtained from the analysis of static earthquake loads with dynamic earthquake loads can be seen seen in Table 5.
Based on the results shown in Table 5 it is known that the period of the structure, base shear, and drift in dynamic earthquake loads for the 3-story and 5-story building structures has a smaller value than the static earthquake load calculated based on equivalent static analysis. The smaller result is caused by the calculation of dynamic linear earthquake load using only the value of the formation of the response spectra of the design which is analyzed using response spectrum analysis in the SAP2000 program. Whereas in the calculation of static earthquake loads, there are enlargements of the coefficients for the calculation of the base shear or seismic base force that guarantee the strength and ductility of the building structure to the lateral force of the earthquake load. But on the contrary the structure of the 7-story building results of the comparison value for the larger base shear and drift is shown by analysis on dynamic earthquake loads. This is due to the static earthquake load calculation for the 7-story building, the value of the seismic response coefficient (Cs) used is maximum, Cs.

Comparison of each floors displacement and allowable displacement inspections
Inter-story drift that occur when the cross section is not allowable to exceed the specified limit. The difference of the inter-story drift must already be multiplied by the deflection magnification factor (Cd) obtained from the choice of structure type. For special moment resisting frame (SMRF) type structures. the Cd value is 5.5. Allowable drift limit in Table 6 of SNI-1726-2012 for structures with a risk category IV of 0.010hsx.
where hsx is the floor height under the floor being reviewed. In this case, the lowest floor height is 4 m. so ∆ a =(0.010×h sx )=(0.010×4)=0.04m=40mm. For floors above it, ∆ a =(0.010×3.5)=0.035m=35 mm. The inter-story drift assessment is shown in the following tables. Based on the comparison results between static earthquake loads and dynamic earthquake loads and drifts that occur, it can be seen most have met the allowable drift limit for each type of building structure. With a 30 MPa concrete compressive strength used to obtain a more efficient cross-sectional dimension of the structure, has met the requirements for earthquake resistance planning for building structures in accordance with SNI-1726-2012 [6]. The material quality and geometry data can be shown in Table 9. Thus the structure of the building can withstand tsunami loads.

Tsunami load calculation
Using calculation steps that refer to FEMA P646 of 2012, the results of calculations for tsunami forces with maximum elevation parameters of different inundation at each type of building height are shown in Table 10.

Apply forces to the structure
The application of tsunami forces for each type of building height is adjusted to the combination tsunami load 1 (T1) and combination tsunami 2 (T2) as shown in the following Figure 2 and Figure 3.

Comparison of internal Forces due to Earthquake Load Combination Tsunami 1 (T1) and Combination Tsunami 2 (T2)
Comparison of internal forces includes moment (M), shear force (D), and axial force (N) for columns while for beams only (M) and (D). Due to the assumption of the arrival of tsunami waves from the x-axis direction, therefore to compare the results of internal forces for earthquake loads, T1, and T2 uses load combinations of 1.2D+1.0L+1.0Ex+0.3Ey for earthquake loads and 1.2D+1Ts+1Lref+0.25L for tsunami load. An evaluation of the results of the analysis is carried out on the values of the internal forces for the first floor column viewed from the exterior column namely column 1 on Grid and interior column. i.e. column on Grid 4 and for the beam being reviewed namely Grid 1 beam and Grid 4 beam. For a clearer picture of the position of the reviewed column and beam elements can be seen in Figure 4.
The purpose of the evaluation on the comparison of maximum internal forces on column and beam elements in terms of the 3-story. 5-story and 7-story building structure is to find out how the structure behaves at each column and beam position in terms of earthquake loads T1 and Q2.
The maximum internal forces of the column on the first floor shown in Table 11 show that the maximum moment in the column lying in column Grid B-1 for earthquake loads and T1. This is because the column in that position carries the greatest axial load coupled with the presence of lateral force from an earthquake and tsunami loads. Whereas at T2 the maximum moment lies in the Grid B-4 column because of the impact load acting on the column in that position. The maximum shear force for earthquake loads and T1 lies in the Grid C-1 column because in that column it con-tinues the lateral load from the Grid A-1 column and the Grid B-2 column. so that the column at the very back of the structure towards the direction of the tsunami wave is carrying greatest shear force. At T2 the maximum shear force lies in the Grid A-4 column because the collision load works directly on the column in that position.
The maximum axial force for earthquake loads is in the Grid B-4 column due to greater axial load from the dead load (DL) and live load (LL) when compared to the columns located on Grid A and Grid C, whereas the maximum axial force for T1 and T2 lies in the Grid C. This column is caused by the large lateral force received by the front column which was hit by a tsunami inundation so as if there was a leverage effect on the structure; thus giving a lifting effect to the Grid A column so that the column in Grid C receives a compressive effect which adds to the amount of axial force received by the column at that position.     Figure 7. Drift graph of a 7-storey building

Drift and Drift Ratio
Results of story drift from the analysis due to earthquake loading, T1, and T2 in the building structure can then be calculated as drift ratio. The drift ratio is the ratio of drift between levels (Δ) and level height (h). Maximum drift in a combination of earthquake loads used drifts that have been multiplied by the deflection magnification factor (Cd) which has been calculated so as not to exceed the allowable inter-story drift limit in accordance with Table  16 of SNI-1726-2012 while the results of drift for tsunami loads are obtained directly from the analysis results of structure in the SAP2000 program. Drift ratio comparison graphs between earthquake loads, T1, and T2 for building types with a height of 3 floors, 5 floors, and 7 floors are shown respectively in Figure 3, Figure 4 and Figure 5, while the drift ratio is presented in Table 12, Table 13, and Table 14.
In the 3-story building structure, drift values due to earthquake loads, T1, and T2 still meet the allowable inter-story drifts. The maximum drift ratio value on the first floor of a 3-story building structure due to earthquake loads, T1, and T2 are 0.75%, 0.52%, and 1.01%, respectively, which are all smaller than the building drift ratio limit with a IV-risk category that is equal to 1%.
In the structure of buildings 5 and 7 floors, the value of the drift ratio on the first floor due to earthquake load has fulfilled the requirements (<1%). but conversely due to the load T1 and T2 at the same floor level. the drift ratio of 5-storey buildings is respectively 1.44% and 2.13%. while in the 7-story building respectively 2.88% and 4.67%.

CONCLUSION
From the results of research and discussion on the effect of earthquake and tsunami loads on the behavior of reinforced concrete structures, evaluation of the analysis