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Structural Evaluation of a Low-Rise Steel
Building in Jakarta
Indrawati Sumeru1*, Suradjin Sutjipto2, William Supardjo3, Sherrica Augustin Sucipto4
1,2Universitas Trisakti, West Jakarta, DKI Jakarta, Indonesia
3,4Suradjin
SUTJIPTO, Inc., West Jakarta, DKI Jakarta, Indonesia
Email : indrawati@trisakti.ac.id
ABSTRACT
Due to increasing awareness of human safety, Indonesia has mandated that all operational
buildings obtain a Certificate of Occupancy. Consequently, existing structures must undergo a structural assessment before being granted
this certificate. Evaluating older buildings poses significant challenges, especially when comprehensive records are lacking, and budgets
do not allow for Non-Destructive Testing
(NDT). This study presents the structural evaluation findings of a three-story steel building in Jakarta. Using visual inspections, field measurements, and limited available
data, an analytical model representing the building's actual condition was developed.
The evaluation followed three procedures: Tier 1 and Tier
2 evaluations of ASCE 41-17
and proportional seismic forces. These procedures aimed to gauge
the structural integrity and identify
areas vulnerable to failure during
a severe earthquake. The assessment focused on the ductility
of the seismic
force-resisting system components and the strength of
beam-column joint connections against specified acceptance criteria. The findings highlight critical insights into the
building’s structural performance, informing decisions on necessary
measures such as structural reinforcement, occupancy restrictions, or demolition. This study underscores the importance of thorough structural
assessments in ensuring the safety and
resilience of older buildings in earthquake-prone regions.
Keywords: ASCE 41; Existing Building Evaluation; Proportional Seismic Forces;
Steel Building.
INTRODUCTION
Lately, structural evaluation work for the purpose
of obtaining a Certificate of Occupancy has been increasingly performed in major cities and
industrial areas across Indonesia
Assessing the structures of existing
buildings is not an easy task.
Drawings and as-built reports containing
information on structural systems, foundation systems, and material specifications are rarely available
The purpose of this research is
to share the experience of conducting assessments
on low-rise steel structure buildings located in Jakarta, with very limited
data and without conducting any tests. The seismic analysis and evaluation
were carried out based on ASCE 41-17 (awaiting its official
version in SNI) and relevant Indonesian National Standards
(SNI) for buildings, including SNI 1729:2020, SNI 7860:2020, SNI 7972:2020, SNI
1726:2019, and SNI 1727:2020
A three-story steel
structure building owned by one
of the private
universities will represent the existing
low-rise steel structure buildings in Jakarta, serving as a case study building in this paper
For facade alterations
and room function conversions, structural analysis and evaluation are conducted based on the latest
loading regulations (SNI
1727:2020) using Tier 1 and Tier 2 evaluations
from ASCE 41-17, as well as
the proportional seismic force method
developed by the author's team
It is important to note
that this structural assessment is conducted solely
based on data obtained from visual observations on-site, without conducting Destructive Tests (DT) or Non-Destructive Tests (NDT), and relying on construction
knowledge from the 1980s, without any existing structural
reports or drawings
This study aims
to provide insights into the
structural assessment process under constraints
of minimal data availability,
relying on visual site observations and historical construction knowledge, without existing structural reports or drawings. The findings and methodologies
discussed herein are intended to contribute
to the body
of knowledge on structural evaluation
practices for low-rise buildings in seismic regions, particularly in developing countries where such limitations are common.
RESEARCH
METHODS
The research uses three methods to evaluate the seismic performance of
existing buildings. It follows Tier 1 and Tier 2 evaluations from ASCE 41-17
standards. Tier 1 involves using a checklist covering structural integrity and
earthquake resistance. Some checklist items can be checked visually, like
spotting structural damage. But for others, calculations using ASCE 41-17
formulas are needed, like checking if load-bearing parts are strong enough
against earthquakes.
After Tier 1 evaluation, Tier 2 evaluation is needed to evaluate any
deficiencies identified in Tier 1. But Tier 2 has different criteria, needing a
more detailed approach. Here, a mathematical model is used to analyze how Tier
1 issues affect the building. This could mean testing different earthquake
scenarios to see how the structure holds up. The goal is to fully understand
the building's earthquake resistance and identify where precaution or
strengthening are needed.
The research also introduces the idea of proportional seismic force as
an additional method. Based on pushover analysis principles, it gives us a look
at how strong existing buildings are. Its goal is to show how buildings perform
if they don't meet ASCE 41-47 standards. By applying earthquake forces
gradually and studying how the building reacts, this analysis uncovers
potential failure mechanisms and structural vulnerabilities.
Basically, the research combines these methods to provide a complete
framework for evaluating the seismic resistance of existing buildings. By
carefully studying and analyzing, it aims to inform necessary precautions or
strengthening to enhance overall structural safety.
RESULTS AND
DISCUSSION
Structural System
From
the visual observations and measurements conducted on-site, it is revealed that
the case study building utilizes a moment steel frame with a wooden floor
structure. The structural system plan of a typical floor is shown in Figure 1.
Figure 1 . Structural System Plan of Typical
Floor
Figure 2 shows
the building's structural system in the longitudinal direction, which consists of alternating moment frames connected
by beams with pinned joints
at both ends.
The column arrangement forms an H-shape
section - King Cross - King
Cross pattern, repeated along the outer side
of the building.
Meanwhile, Figure 3 illustrates the building's structural system in the transverse
direction, which consists of a series
of moment frames with a gable
frame on top. At each rigid frame,
both ends of the beam
are equipped with haunches made from
the W-shape beam sections.
Figure 2. Structural System Section in Longitudinal Direction
Figure 3. Structural System Sections in Transverse
Direction
Structural System Analysis
The mathematical
model of the building's structural system, analyzed by ETABS software, is shown in Figure
4. The haunches of the beams, which
are part of the lateral force-resisting system, are accurately modeled to match
the existing conditions. This is intended to
achieve a building behavior closer to the actual
conditions. All column supports at the
building base are assumed to be
pinned joints in accordance with design practices in the 1980s era.
Figure 4. ETABS Mathematical Model
Figure 5 illustrates
the case study building dynamic analysis results. The first and third
modes are translational modes, while the
second mode is a rotational mode. This indicates that the building’s behavior is less
ideal, and it is sensitive to
torsion.
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(a) |
(b) |
(c) |
Figure 5. Mode shapes (a) Translation X Direction;
(b) Rotation; (c) Translation
Y Direction
With this
mathematical model, an examination of irregularities in the building's structural system was then
conducted, as shown in Table 1, according to the provisions
of Table 13 and Table 14 of
SNI 1726:2019, along with other relevant articles. The examination results indicate the presence of
horizontal irregularities such
as torsional, extreme torsional, and reentrant corner irregularities, as well as vertical irregularities such as stiffness-soft story irregularity.
The extreme
torsional horizontal irregularity
and the stiffness-soft
story vertical irregularity indicate that the behavior
of the building's
structural system is less favorable
due to excessive
torsional tendencies and the potential
for soft story hazards. Both of these
should be avoided when designing
the building. We need to take
into account that in the 1980s, building designs generally relied on two-dimensional static analysis, and Indonesian steel regulations did not yet incorporate seismic design requirements. Therefore, torsion and soft
story issues were likely not detected at that time.
Table 1. Irregularity
Condition of Structure
Evaluation Based On The
Latest SNI for Steel Structures
Based on the provisions of SNI 1726:2019, any structure located
in Jakarta will be classified into Seismic Design Category D and is required
to use a special moment frame, as specified in Table 12 of SNI 1726:2019. As a consequence, beams, and columns that
are part of the lateral force-resisting system shall meet
the requirements outlined in Section E3.6b of SNI 7860:2020. These requirements mandate that these structural
elements be classified as Highly Ductile (HD) members.
To classify beams and columns as Highly Ductile (HD) members, the b/tf and h/tw ratios shall meet two
requirements: first, they shall meet
the compactness criteria according to Table B4.1 of
SNI 1729:2020, and second, they shall meet
the Highly Ductile (HD) requirements listed in Table D1.1 of SNI 7860:2020. Both of these requirements
need to be
met to ensure
that the elements can avoid
premature fracture, which leads to
low cyclic resistance, thus preventing them from developing a 4% rotation capacity, as local buckling will occur before
the formation of plastic hinges.
From the
information provided in Table 2, it can
be seen that
only the W200x100 beam meets the
requirements as a compact and Highly Ductile
(HD) section, while the W300x150 and W350x175 beams only meet
the requirements as a compact and Moderately
Ductile (MD) section.
Table 2. Ductility
Condition of Beams (Ry = 1.5)
Next, from the
data in Table 3, it can be observed
that all columns only meet
the requirements as a compact and Moderately
Ductile (MD) section.
Table 3. Ductility Condition
of Columns (Ry = 1.5)
The beam-column connections, which are part of the special
moment frames, are required to meet
the provisions outlined in Section E3.6c of SNI 7860:2020. These requirements mandate the use of
prequalified connections referring to SNI 7972:2020.
Figure 6 shows that
the existing beam-column connections use an end
plate connection system with haunches
both in the transverse and longitudinal directions of the
building. These connection types cannot be classified
as prequalified end plate connections according to the
provisions in SNI 7972:2020.
Figure 6. Existing Condition of Beam-Column Joint
Connection
Building
Performance Level
Taking into account
the age and
existing condition of the building,
it has been decided that the
desired level of building performance to be achieved
is the Limited
Performance Objectives. It is the lowest
level of the evaluation of the
existing building in ASCE
41-17.
To achieve the Limited
Performance Objectives level as per ASCE 41-17, this building needs
to meet the
Life Safety structural performance requirements at the BSE-1E seismic
level, which refers to an earthquake
with a return period of 225 years
(as indicated by the blue line
in Figure 7). However, the evaluation results indicate that the structural
performance requirements cannot be met.
Therefore, the structural performance is downgraded to
Collapse Prevention but still at
the BSE-1E (225-year) seismic
level. The evaluation of this downgraded structural performance will be further
explained in this paper.
Figure 7. Spectrum Response Graphs (MCER,
BSE-2E and BSE-1E)
Tier 1 Evaluation
The focus of the
Tier 1 Evaluation of ASCE 41-17 is on a quick assessment
through visual observations
on-site and available construction data. Evaluation is conducted
by filling out forms that
include several simple calculations, the formulas for
which are provided in ASCE
41-17.
Table 4 . Tier 1 Evaluation
Result
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Figure 8. Collapse Prevention Basic Configuration
Checklist
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Figure 9 . Collapse Prevention Structural Checklist
As shown in Figures 8 and 9, Tier 1 Evaluation
identifies 9 types of deficiencies: torsion, drift check, diagonally sheathed and unblocked
diaphragms, interfering walls, soft story,
ties between foundation elements, strong column-weak beam, moment-resisting connections, and panel zones. All identified deficiencies must be re-evaluated using Tier 2 by
applying all the consequences required by ASCE 41-17 for each deficiency.
Tier 2 Evaluation
Tier 2 Evaluation of
ASCE 41-17 provides a more specific analysis compared to Tier
1. According to the provisions in ASCE 41-17 for Tier 2 Evaluation,
only the deficiencies from Tier 1 Evaluation needed to be
evaluated. A representative
analysis model is required to conduct
Tier 2 Evaluation, taking into account
all the consequences
of deficiencies from Tier 1 Evaluation
to obtain the forces acting
on the structural
elements during a BSE-1 seismic level (225-year return period). Subsequently, the forces acting
are compared with the amplified structural
element capacities as per the provisions of ASCE 41-17.
As shown in Table 5, beam-column connection is the only
item that still indicates failure. Thus, the remaining
deficiency after conducting Tier 2 Evaluation is the
beam-column connection and inter-story drift due to
connection failure.
If referring to the
steps in ASCE 41-17, all deficiencies at Tier 2 need to
be re-evaluated with Tier 3 using
nonlinear analysis. However, nonlinear analysis does not accommodate connection checks. Therefore, the evaluation is stopped at
Tier 2 of ASCE 41-17.
Table 5. Tier 2 Evaluation
Result
Proportional Seismic Force Method
After evaluating the latest building standards in Indonesia (SNI) and
ASCE 41-17, it is apparent that the
structure does not meet the permissible
acceptance criteria, especially regarding connections and structural deformations. With the understanding
that significant deformations can be acceptable if
the structural element's strength can accommodate them, inspired by the pushover
analysis, the concept of proportional
seismic force is introduced to
assess the actual performance of buildings that
cannot meet the acceptance criteria of both
new and existing
building regulations.
The requirement that shall be maintained
in the concept of proportional seismic force is
the ductility of the elements.
These elements shall meet the
ductility provisions specified in the latest building design regulations. However, based on the analysis
results listed in Table 2 and Table
3, the structural elements of this
building do not meet these ductility
requirements. It is important to
note that the Ry value used in these
checks was 1.5, as required by the
latest building regulations. However, it should be
remembered that this building was
not designed in this decade but rather
in the 1980s when steel production specifications differed from current standards.
Therefore, it is considered to
use the Ry
value specified in ASCE
41-17 for steel materials produced in the period from
1961 to 1990, which is 1.1.
As shown in Table 6 and Table 7, almost
all elements have met the
ductility requirements, with only the
column elements failing to meet
the ductility requirements by just 1%. Based on these results,
it is believed
that further analysis and evaluation
using the proportional seismic force concept are still feasible.
Table 6. Ductility
Condition of Beams (Ry = 1.1)
Table 7. Ductility
Condition of Columns (Ry = 1.1)
After a series
of extensive trials, by adjusting
the seismic force reduction factor, a reduction factor was obtained
that did not result in failure at the connections
and was able
to meet the
requirements for inelastic deformation of the structure,
which is 12.5, as shown in Table 8. Although not included in this paper, it
is actually possible to obtain
the earthquake return period value
that the building can withstand.
Table 8. Comparison of
Results between SNI
1726:2019 and Proportional Seismic Forces
Figure 10. Comparison of Seismic Levels
CONCLUSION
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Copyright holder: Indrawati
Sumeru, Suradjin Sutjipto,
William Supardjo, Sherrica
Augustin Sucipto (2024) |
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First publication right: Asian
Journal of Engineering, Social and Health (AJESH) |
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