The Effect of Seismic Masses in Calculation of a 17 Multi-story

Concrete Structure

Daud Rahmat Wiyono

, Roi Milyardi

, Yosafat Aji Pranata

and Robby Y. Tallar

Department of Civil Engineering, Maranatha Christian University, Jl. Surya Sumantri 65, Bandung, Indonesia

robby.yt@eng.maranatha.edu

Keywords: Mass Source, Self and Specified Mass, from Loads, Equivalent Lateral Force, Story Shear, Story Drift.

Abstract: The seismic weight according to code will be used for seismic calculation and defined by mass source. The

application in ETABS has a 3-ways to define seismic mass: 1. From self and specified mass, 2. From loads.

3. From self and specified mass and loads. If the mass source is not defined properly, seismic forces will not

be calculated correctly and so the base shear value will also be incorrect. The purpose of this article is to

obtain the mass source from 3-ways in ETABS which is near to the manually calculated Mass and its effects.

The case study is a 17 multi-story building

, and from the results of the analysis and discussion it is concluded

that: the lowest time period, equivalent lateral force, story shear, story drift are the ‘From self and specified

mass’, followed by the ‘From load with DL+0.5 LL’. Next is the ‘Self and specified mass and load with

DL+0.5 LL’, and the last is ‘Self and specified mass and load with DL+ LL’. The value of ‘From load with

DL+0.5 LL’ is near to the manually calculated Mass with ‘DL+LL’, and thus corresponds to the

recommendation by ASCE 7–10.

1 INTRODUCTION

Mass source is a seismic weight according to code

and performed for seismic analysis. ASCE 7–10

requires the effective seismic weight including dead

load and other load, in this case other load is LL

reduction, so the value of reduction factor f is for LL

is determined. The load here will be used for seismic

calculations. In the application of software ETABS

there are 3 ways to define seismic mass: 1. From self

and specified mass, 2. From loads. 3. From self and

specified mass and loads.

Each choice has different consequences in

inputting Self weight, Dead load and Live load. For

example if From loads is chosen then the load S can

be assigned that refer to dead weight type (self-weight

included) and also the live load cases as per code with

the appropriate factor based on governing condition

(Computers and Structures Inc., n.d.).

The purpose of this article is to obtain the mass

source with a near to mass calculated manual from 3-

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ways option in ETABS. The case study is a 17 multi-

story building where until the 10

story, the mass

becomes one mass and from the 11

to the 17

story,

the mass becomes 2-tower and the structure will be a

dual system.

ASCE 7–10 use ‘DL + 0.25 LL’ for seismic

masses, which LL for gravity combination can reduce

with factor 0.5. The seismic weight/mass that is

calculated using ETABS is then verified using an

analytical method which is called Mass calculated

manual. Self-weight has default of ‘DL + f LL’,

Specified Load patterns must select ‘DL + f LL’, and

additional mass due to surface loads line loads.

In ETABS consider full (100%) of dead load and

25% of live load (less than 3kN/m

), and if the live

load exceeds 3kN/m

then the mass source will be full

(100 %) of dead load and 50 % of live load. Usually

only full of dead load is enough for normal buildings,

but needed to consider all the Live loads and Dead

loads that are permanent. For example permanent

mechanical equipment as live load then consider

184

Wiyono, D., Milyardi, R., Pranata, Y. and Tallar, R.

The Effect of Seismic Masses in Calculation of a 17 Multi-story Concrete Structure.

DOI: 10.5220/0010747800003113

In Proceedings of the 1st International Conference on Emerging Issues in Technology, Engineering and Science (ICE-TES 2021), pages 184-189

ISBN: 978-989-758-601-9

 2022 by SCITEPRESS – Science and Technology Publications, Lda. All rights reser ved

them in mass source too. If a portion of live load is

assumed to be sustained for example where LL is

heavy like in malls, a portion of LL should also be

considered. So, any load that is deemed to be

permanent needs to be considered in seismic

calculation (Akis, 2004; Nageh, 2007).

These 3-ways choices each have the purpose to

input the load cases in each choice. Everyone can use

each 3-way choice with different load cases. The load

option is the one generally recommended by people

familiar with ETABS. The reason is because the

default “From self and specified mass” option means

that additional mass has to be manually assigned, and

that involves unit conversion for mass assignments.

The third option “From self and specified mass

and loads” is dangerous because many users tend to

include the dead self-weight in that list, thereby

double counting self-weight in the mass model. The

users can detect it in the warning while checking the

model showing the sentence “Mass source has both

element self-mass and a load pattern with a self-

weight multiplier greater than zero. This may result

in duplicated self-mass. If it is true, while checking

the model it will show the sentence “Model has been

checked”, and no warning messages were generated.

2 LITERATURE STUDY

Mass values consist of structural elements which

have volume and material density. In dynamic

analysis, mass translation and rotation with

acceleration to create inertial forces. For the purpose

of estimating seismic loads standard ASCE 7-10

requires calculating the effective seismic weight

which includes dead load, partitions and permanent

equipment, plus 25% of the floor live load in areas

used for storage (MacLeod, 1970; Somers, 2012;

Wight & MacGregor, 2012).

This contribution of live load as inertia seems to

be correlated with the low likelihood that live load

objects be present at the time of the designed

earthquake. However, for storage and some

commercial facilities live loads may continuously be

present and even exceed the dead load. Seismic mass

source is a parameter that used both for calculation of

seismic loads using Equivalent Lateral Force Method

and Responses Spectrum Analysis (American Society

of Civil Engineering, 2010; Atkins Structural

Department, 2007; Budiono & Supriatna, 2011;

Wiyono, R.D., Roi, C. M., & Lesmana, 2018).

Mass source is the structural weight and the

seismic loads are calculated based on the specified

mass of the building. ASCE 7/IBC requires for

another load as storage which is 0.25LL (not be

included in the effective seismic weight if increasing

of storage loads adds no more than 0.05, garages and

parking need not be included in the effective seismic

weight. Partition weight (10 psf) is required and the

weight of operation of permanent equipment. The

loading combination of 1.2D + E + 0.5L + 0.25S for

all occupancies in accordance with Table 4-1 ASCE

7–10 less than or equal to 4,79kN/m

3 ANALYTICAL MODEL

In this case study, a 17 multi-story building with two

elevator shafts in the left side and the right side of

floor plan building load has been calculated from the

code (American Society of Civil Engineering, 2010;

Badan Standarisasi Nasional, 2012). The mass source

until the 10th story is one mass. After that from the

to the 17

floor, the mass will become two

towers. The 3D structure given in Figure 1 shows the

plan of each floor.

(1a) 3D building model (1b) 1

-4

Floor Plan

(1c) 5

-6

Floor Plan (1d) 7

-17

Floor Pla

Figure 1: Building model and floor plane data.

4 RESULTS AND DISCUSSION

Table 1 shows the manually calculated Mass and in

Table 2 is shown the time periods. The lowest time

period is ‘From self and specified mass’, after that

‘From load with DL + 0.5 LL’, next is the ‘Self and

specified mass and load with DL + 0.5 LL’, and the

last is ‘Self and specified mass and load with 1 LL’.

From this table can be seen that the period of Mass

calculated manual DL + LL is near to From load with

DL + 0.5 LL.

The Effect of Seismic Masses in Calculation of a 17 Multi-story Concrete Structure

185

Table 1: Manual Calculation of Mass.

Floor

Self-Weight (DL)

(kg/m

)

SDL

(kg/m

)

(kg/m

)

Total

Area

(

)

Total Weight

(kg)

17 27072 150 250 94 64672

16 65952 150 250 229 157552

15 222912 150 250 774 532512

14 222912 150 250 774 532512

13 222912 150 250 774 532512

12 222912 150 250 774 532512

11 222912 150 250 774 532512

10 222912 150 250 774 532512

9 273600 150 250 950 653600

8 269856 150 250 937 644656

7 269856 150 250 937 644656

6 269856 150 250 937 644656

5 338112 150 500 1174 1101212

4 522144 150 500 1813 1700594

3 360864 150 500 1253 1175314

2 262368 150 500 911 854518

1 608904 0 500 1933 1575404

0 642132 0 500 1836.2 1560232

Figure 2: Variation of mass source.

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186

Figure 3: Variation ofequivalent lateral forces.

Figure 4: Story shear with variation mass source.

Figure 5: Story drift with variation mass source.

The Effect of Seismic Masses in Calculation of a 17 Multi-story Concrete Structure

187

Table 2: Time Period from Varian Masses.

Mode

1 2 3

Mass Source Condition

Self and Specified Mass

Default DL + LL

1.41

1.04

0.7

From Loads

DL + 0.5 LL

1.73

1.30

0.8

Self and Specified Mass and

Loads

DL + 0.5 LL

2.23

1.67

1.1

Self and Specified Mass and

Loads

DL + LL

2.29

1.72

1.1

Mass Source Manual

DL + LL

1.7

Figure 2 shows the mass sources. The mass is

calculated manually as a comparison. So, from the

value of ‘Self and specified’, the mass is 22.10%

lower. The value of ‘From load with DL + 0.5 LL’ is

2.75% bigger than the value of ‘Self and specified’

mass. The ‘load with DL + 0.5 LL’ is 72.43% and

the ‘Self and specified mass and load with DL + LL’

is 84.42%.

Figure 3 shows the Equivalent Lateral Load. The

mass is manually calculated as comparison. The value

of ‘From self and specified mass’ is 47.28% lower.

The value of ‘From load with DL + 0.5 LL’ is 2.11%

bigger. The value of ‘Self and specified mass and load

with DL + 0.5 LL’ is 71.57% and the value of ‘Self

and specified mass and load with DL + LL’ is

84.19%.

Figure 4 shows the story shear. Because the value

of ‘Mass manually calculated Dl + LL’ is near to the

value of ‘From load with DL + 0.5 LL’, so it is

assumed that the value of Story shear of ‘From load’

is the same as the comparison. And thus, the value of

‘From self and specified mass’ is 28,56 % lower. The

value of ‘Self and specified mass and load with DL +

0.5 LL’ is 64,16% and finally the value of ‘Self and

specified mass and load with DL + LL’ is 72,75%.

Figure 5 shows the story drift. Because the ‘Mass

calculated manual DL + LL’ is near to the ‘From load

with DL + 0.5 LL’, it is assumed that the value of

‘Story drift From load with DL + LL’ is the same as

the comparison. So, the value of ‘From self and

specified mass’ is 27,25% lower, then the value of

‘Self and specified mass and load with DL + 0.5 LL’

is 47,64%. And finally the value of ‘Self and specified

mass and load with DL + LL’ is 51,94%.

4 CONCLUSIONS

From the results of the analysis and discussion it is

concluded that:

1. The lowest time period is ‘From self’ and

‘specified mass’, after that ‘From load with DL

+0.5 LL’, next is the ‘Self and specified mass and

load with DL + 0.5 LL’, the last is ‘Self and

specified mass and load with DL + LL’. From

Table 2 can be seen that the period of ‘Mass

calculated manual DL + LL’ is near to ‘From load

with DL + 0.5 LL’.

2. Based on the Chosen Mass which is manually

calculated ‘DL + LL’ as the comparison, the value

of ‘From self and specified’ mass is 22.10%

lower, then the value of ‘From load with DL + 0.5

LL’ is bigger 2.75%, followed by the ‘Self and

specified mass and load with DL + 0.5 LL’ which

is 72.43 % and finally the value of ‘Self and

specified mass and load with DL + LL’, which is

84.42%.

3. If the Mass is manually calculated ‘DL + LL’ as a

comparison of the Equivalent Lateral Force, the

value of ‘From self and specified mass’ is 47.28%

lower, then the ‘From load with DL + 0.5 LL’,

which is 2.11% bigger/. Followed by the value of

‘Self and specified mass and load with DL + 0.5

LL’, which is 71.57% and finally the value of

‘Self and specified mass and load with DL + LL’

which is 84.19%.

4. Because the Mass which is manually calculated

‘DL + LL’ is near to the value of ‘From load with

DL + 0.5 LL’, it is assumed that the value of 'Story

shear of the From load is the same as the

comparison. The value of ‘Self and specified

mass’ is 28.56% lower, followed then by the value

of ‘Self and specified mass and load with DL +

0.5 LL’ which is 64.16% and finally the value of

‘Self and specified mass and load with DL + LL’,

which is 72.75%.

5. Because the Mass which is manually calculated

‘DL + LL’ is near to the value of ‘From load with

DL + 0.5 LL’, it is assumed that the value of Story

drift of ‘From load’ is the same and as the

comparison. The value of ‘Self and specified

mass’ is 27.25% lower, followed then by ‘Self and

specified mass and load with DL + 0.5 LL’, which

is 47.64 %, and finally the value of ‘Self and

specified mass and load with DL + LL’, which is

51.94%.

6. Since the model calculation of ‘Load with DL +

0.5 LL’ is near to Mass which is manually

calculated with ‘DL + LL’, it corresponds to the

recommendation of ASCE 7–10.

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