KSCE Journal of Civil Engineering (2016) 20(4):1201-1210 Construction Management

Copyright ⓒ2016 Korean Society of Civil Engineers

DOI 10.1007/s12205-015-0198-2 pISSN 1226-7988, eISSN 1976-3808
www.springer.com/12205
TECHNICAL NOTE

Unit Modular In-Fill Construction Method for High-Rise Buildings

Hyung Keun Park* and Jong-Ho Ock**
Received March 9, 2015/Revised April 30, 2015/Accepted May 19, 2015/Published Online June 22, 2015

··································································································································································································································

Abstract

A modular construction method includes factory-prefabricated room-sized volumetric units. Although low-rise buildings have
been constructed worldwide using this method for more than 30 years, it is a relatively new technology in high-rise construction.
There are three basic methods of constructing high-rise buildings using modular construction: the core method, the core-and-podium
combination method, and the modular in-fill method. While the first two have been used in the USA and in several European
countries, the third method, introduced in 2011 by an international cruise ship development firm, is a rather new approach for which
there are few case histories. Although the modular in-fill method is being used to construct several dormitories in Korea through
public–private partnerships with the Korean government, there have been few applications of this method to construction of high-rise
buildings. Therefore, its applicability and construction feasibility should be verified. As a pilot study to test the applicability of the
modular in-fill method, a 12-story residential building was built in Korea. This paper describes a case study of the pilot project. The
advantages and disadvantages of the method and its applicability in terms of cost effectiveness and construction schedule
management were evaluated. The results of this study provide a reference base for advancement of the in-fill method based on an
analysis of problems that arose during the construction process for the pilot project.
Keywords: prefabricated construction, modular technology, modular in-fill method, cost effectiveness, schedule compression
··································································································································································································································

1. Introduction dormitory expansion projects for public and private university

students, and bachelor housing improvement projects (Korea
Modular construction is different from conventional construction Research Institute for Construction Policy, 2011). To keep pace
in that a considerable proportion of the necessary project components with the growth of the market, it is necessary to develop
are manufactured or built off-site. The Korean domestic construction advanced modular construction techniques, not only for low-rise
industry, like those in other developed countries, has recently buildings but also for high-rise ones.
faced limitations in implementing labor-intensive production Although modular technology has been used for over 30 years
systems, reductions in the construction labor force, and increases to construct low-rise buildings around the world, the technology
in labor costs (Lee and Ock, 2014). As a result, modular construction is relatively new in high-rise construction, and there is increasing
has emerged as an alternative approach to building construction. pressure to extend the technology to construction of buildings of
In modular construction, 80 to 90% of the individual modules 12 stories or more (Lawson and Richard, 2010). Three modular
are manufactured in a controlled off-site factory environment, construction methods have been used to build high-rise buildings:
transported to the building site, and assembled on-site to form a main the core method, the core-and-podium combination method, and
facility. The modules are three-dimensional volumes or rooms the modular in-fill method. While the first two have been used in
rather than prefabricated panels or bathroom pads. the USA and in several European countries since 2005, the third
Compared to those in other developed countries, the Korean so-called Cruise Housing System (CHS), introduced in 2011 by
modular construction market has a relatively short history. From a multi-national cruise ship development EPC (engineering, procure-
2003 to 2011, the market grew to $0.5 billion and was limited to ment, and construction) firm, is a relatively new approach
construction of buildings with four or fewer stories (e.g., schools, (STACO, 2011).
military barracks, and dormitory buildings) because of the The CHS approach has been applied to the construction of a
immaturity of the technology. However, the outlook for the 12-story building and a 16-story hotel in China and has been
market is very positive; it is expected to grow to $1.8 billion by used to design several high-rise student dormitories in Korea
2020 as a result of the current governmental infrastructure through a public–private partnership with the Korean government.
enhancement plan for housing projects for low-income families, However, because there is very little information available

*Member, Professor, School of Civil Engineering, Chungbuk National University, Cheongju 361-763, Korea (E-mail: parkhk@chungbuk.ac.kr)
**Member, Professor, Dept. of Architectural Engineering, Seoul National University of Science & Technology, Seoul 139-743, Korea (Corresponding
Author, E-mail: ockjh@seoultech.ac.kr)

− 1201 −
 Hyung Keun Park and Jong-Ho Ock

concerning the use of this method in high-rise building construction, long (Lu and Korman, 2010), providing 18 to 32 m2 of floor area.
its applicability needs to be verified, and the construction feasibility
of the related techniques has to be evaluated to enhance the 2.2 High-rise Modular Construction Methods
constructability of this method. There are three methods of constructing high-rise buildings
A 12-story student dormitory building has been recently using modular technology: the core method, the core-and-podium
constructed in Korea using CHS as part of a pilot project for a method, and the modular in-fill method. The first two methods
public–private partnership. This study was conducted to assess utilize load-bearing modules, whereas the third method makes
the applicability of CHS from the perspectives of construction use of panel-based modules. Each method is described below.
cost and scheduling by performing a case study of the pilot
project. The benefits of the in-fill method were identified by 2.2.1 Core Method
evaluating the improvements made in addressing issues that have Load-bearing modules are typically used in modular construction
arisen in previous low-rise modular projects in Korea. for buildings up to eight stories high (Cartz and Crosby, 2007).
The design of taller modular buildings requires additional consi-
2. Theoretical Background derations to ensure the overall structural stability of a building.
One technique is to build a concrete core and stack modules
2.1 Module Architecture Classification around the core. The modules are directly connected to the core
The modules are in general classified into two categories by attaching ties to cast-in-place plates in the core, so that
depending on the load-bearing capacity of a module: panel-based compression is vertically transferred through the modules and
modules and load-bearing modules. A panel-based module consists the overall stability of the building depends on the core.
of wall panels and ceiling panels that form a self-standing module Two options for module arrangement using the core method
without any structural components, such as beams or columns. were developed in the United Kingdom (UK) to build a 17-floor
The panels in a panel-based module are connected using project called the Paragon in West London in 2007 (Azari et al.,
mechanical devices and chemical glue. Modules in this category
are not able to transfer loads to each other (Lee and Ock, 2014).
Two categories of load-bearing modules exist: load-bearing
wall types and load-bearing frame types. The load-bearing wall
type has steel studs or pipes spaced at intervals of 300-600 mm
that form four-sided walls, as shown in Fig. 1(a). Modular buildings
of four to eight floors, depending on the size and spacing of the
steel studs used, are typically built with this type of module
(Lawson et al., 2005).
Unlike load-bearing wall-type modules, frame-type modules
transfer vertical loads through beams and pillars, which are
anchored using bolts and weld to each other as shown in Fig.
1(b). For modules of the frame type, because the walls are non-
load-bearing, the corner posts must be aligned and be connected
throughout the building height.
The sizes and shapes of individual modules vary in accordance
with the building design and the locations of the modules in the
building. Each individual module is expected to be self-contained
and waterproof and arrives at the construction site with fixtures
and finishes. A typical module is 3 to 3.6 m wide and 6 to 9 m

Fig. 2. Two Module Arrangements in the Core Method (Lawson

Fig. 1. Load-bearing Modules (Cho, 2013): (a) Bearing Wall Type and Richards, 2010): (a) Core Only Arrangement, (b) Core
(b) Frame Type and Corridor Arrangement

− 1202 − KSCE Journal of Civil Engineering

 Unit Modular In-Fill Construction Method for High-Rise Buildings

2013). The two options differ in the spatial relationship of the

modules around the core, as shown in Fig. 2. With the first
option, the modules are connected directly to the core, whereas
with the second option, horizontal loads are transferred via in-
plane trusses within the corridors and are again connected to the
core. The notation used in Fig. 2 indicates the number of bedrooms
and people for which a module is intended. For example, 2B4P
denotes a residence with two bedrooms for four people.

2.2.2 Core-and-podium Combination Method

Modules can be combined with steel or reinforced concrete
frames and cores to enhance the flexibility of space arrangement
by providing a podium structure. This approach allows successful
construction in situations where the dimensional limits of the
modules would otherwise be too constricting. The modules are
placed on the podium, and the open spaces, along with the
podium, can be used as commercial shops or parking areas.
Examples of this method include a 25-story residential building
in Wolverhampton, UK, a 12-story student residence in Bristol,
UK (Lawson et al., 2012), and a 32-story residential tower called
Atlantic Yards B2 in Brooklyn, New York, USA (Azari et al.,
2013). The Atlantic Yards B2 project was based on the 25-story
Wolverhampton project as a benchmarking model and is believed
to be the tallest modular building in the world.

2.2.3 Modular In-fill Method

This method adapts conventional construction techniques to
building the frames of a facility. Fig. 3 illustrates the construction
procedures involved in the in-fill method. Reinforced concrete,
steel, or precast concrete frames are constructed in the field in
parallel with manufacturing of modules in a factory. The modules,
designed to be independent, are then transported and in-filled
Fig. 3. Procedures for Modular In-fill Construction Method
into the frames on site.
This construction method offers the usual advantages of
modular construction over conventional construction, such as a available (STACO, 2012). Compared to research on low-rise
weatherproof construction environment, fewer on-site truck modular buildings, there has been little research on the issues
deliveries, less on-site equipment, fewer on-site construction associated with construction of high-rise modular buildings.
activities, less construction waste, faster construction, and lower Lawson et al. (2012) conducted case studies on several high-
overall cost, while mitigating uncertainty concerning the overall rise modular buildings built in the UK. The study addressed such
structural stability of the high-rise modular building. technical aspects of the core method and the core-and-podium
The structural behavior of high-rise modular assemblies is combination method as the construction data, deliveries, waste,
very complex because of the influences of eccentricities and sustainability, and economic benefits of modular construction,
tolerances in the module installation operation and the mechanism and summarized the lessons learned. Lawson and Richard (2010)
of horizontal force transfer to the core. By utilizing traditional presented technical information on load-bearing modular walls
construction methods to build the frames of a facility, the in-fill and the structural action of groups of modules in high-rise
method enhances confidence in that the overall structural modular buildings obtained through in-depth experimentation.
stability of a building is ensured. Lee and Ock (2014) performed research on the modular in-fill
method along with CHS. The study introduced the typical
2.3 Previous Studies construction procedures for use of the method with precast
Although two modular in-fill construction projects have been concrete and reinforced concrete structures. While the distinctive
completed in China, a 12-story hotel and a 16-story hotel in the characteristics of the in-filled method were compared with
cities of Hangzhou and Suzhou, respectively, the details of the traditional construction methods and with the core method in the
results of these construction projects, such as schedule compression, research, the amounts of schedule compression and cost savings
budget savings, and quality assurance achieved, are not publicly achieved were not analyzed because of the lack of real-world

Vol. 20, No. 4 / May 2016 − 1203 −

 Hyung Keun Park and Jong-Ho Ock

construction data.

3. Case Study of the In-fill Method

This study was conducted to assess the applicability of the in-

filled method from diverse technical and managerial points of
view by performing a case study. The case study subject was a
12-story apartment building in Korea recently constructed using
the CHS approach. The building has one basement floor and 12
superstructure floors, for a total of 3,700 m2 of floor area. The
frames of the building are made of reinforced concrete structures.
Fig. 5. Wall and Ceiling Panels of the Modules (STACO, 2012): (a)
The first three floors are occupied by shops, and the fourth Wall Panels, (b) Ceiling Panels
through twelfth floors are designed as apartments built along
with in-filled unit-modules. Fig. 4 shows a typical floor plan of
the project. coating finish. The insides of the panels were filled with mineral
Three types of unit modules were manufactured for the wool, which provides excellent insulation and noise cancellation.
building, based on the CHS standard unit-module of width × The panel-to-panel joints were clip joints made of iron.
length = 3,000 mm × 6,000 mm for a one-room apartment (A in The dimensions of the ceiling panels were length × width ×
Fig. 4), a two-room apartment (B in Fig. 4), and two bedrooms thickness = 2,400 mm × 300 mm or 600 mm (two widths) × 25,
with a living room (C in Fig. 4). To satisfy the local building- 40, 50, 60, or 75 mm (five thicknesses). The ceiling panels were
coverage-ratio limit of 60%, the modules were manufactured in produced in various shapes and sizes for various purposes. Both
slightly larger sizes than the CHS standard, i.e., 3,250 mm × the wall and ceiling panels had an error tolerance of 0.5 mm for
6,200 mm, 3,050 × 6,150 mm, 3,100 mm × 6,150 mm, and 3,100 the width and thickness and 3 mm for the length. Quality
mm × 6,200 mm, for a building coverage ratio of 59.84%. The assurance was performed to ensure that each panel would be
unit modules were uniformly 2,500 mm in height, and a total of within the tolerance range.
67 modules were in-filled. The modules were manufactured according to the orders
shown in Fig. 6. Each module consisted of a living room unit and
3.1 Prefabrication of Unit-Modules a toilet unit. The toilet unit was manufactured separately from the
Figure 5 illustrates the walls and ceiling panels used in the living room unit. The location of the bathroom unit is shown in A
CHS construction. The wall panels were sized at length × width and B in Fig. 4. Fig. 7 illustrated the combination of a bathroom
× thickness = 2,200 mm × 600 mm × 25 mm, 30 mm, 50 mm, or
75 mm (four thicknesses). The panels had a galvanized steel
exterior sheet 0.6 mm thick with a Polyvinyl Chloride (PVC) film

Fig. 6. Module Manufacturing Process: (a) Floor Frame Installa-

tion, (b) Floor Panel Installation, (c) Wall Panel Installation,
(d) Interior Furniture Installation, (e) MEP Units Installation,
Fig. 4. Floor plan of the Pilot Project (f) Ceiling Panel Installation

− 1204 − KSCE Journal of Civil Engineering

 Unit Modular In-Fill Construction Method for High-Rise Buildings

lifting of the modules, a balance bar was used to prevent twisting

(Fig. 8(a)). The modules to be in-filled first were the first priority
for transportation and installed as soon as they arrived on-site to
avoid problems such as moving line congestion and overstock of
the modules on-site.
Figure 8 illustrates the module installation process, from loading
a module into a truck at the factory ((a) and (b)) to setting a
module in a building frame at the jobsite ((g) and (h)). Figs. 8(c),
(d), and (e) illustrate lifting a module to the building frame with a
lifting device. Figs. 8(f) and (g) illustrate that the device was
fixed to the edge of the installation target floor.

3.3 Unit-Module Installation

Fig. 7. Bottom Plate of Modular Unit (STACO, 2012)
The modules were moved to the appropriate installation locations
using a moving zig and a forklift (Fig. 8(h)). The moving zig is
unit with a living room unit. The bathroom floor was lower than the shown in front of the lifting device in Fig. 8(g). Workers were
living room space to prevent flooding from the bathroom side. able to perform the loading and unloading of the modules into
the lifting device easily because a roller was installed at the
3.2 Transportation and Lifting bottom of the device.
The prefabricated modules were transported from the factory Figure 9 illustrates the 3.2T-150 × 50 × 20 C-channel section
by a 10-ton truck after installation of anti-swing devices to shown in Fig. 7. These illustrations show how a module was
prevent any damage from occurring during transportation. During fixed by means of a moving zig. As shown in Fig. 9(a), a module
was moved to an installation location by a moving zig. The
lifting device then lifted up the module with a hydraulic system,
and the zig was removed. The module was secured on the slab
using anchor bolts, as shown in Fig. 9(c).

3.4 Construction Duration Analysis

The pilot building construction commenced in April of 2011
and was completed ten months later in January 2012. At the

Fig. 8. Steps in Transporting and Installing Modules: (a) Loading

with Balance Bars, (b) Loading on a Truck, (c) Arriving at
Job-site, (d) Operating a Lift Device, (e) Preparing a lifting, Fig. 9. Moving Zig Operation to Fix Modules: (a) Operating a Mov-
(f) Inserting into a Frame, (g) Fixing at the Frame Edge, (h) ing, (b) Removing a Moving Zig, (c) Anchoring a Module to
Installing a Module. a Slab

Vol. 20, No. 4 / May 2016 − 1205 −

 Hyung Keun Park and Jong-Ho Ock

beginning of the project, a project management team was formed cost of manufacturing 67 modules and installing those on site
with engineers from the CHS design, production, and construction totaled $1,617,700, which corresponds to a unit cost per module
divisions. The project management team initially anticipated that of $24,140 (or approximately $1,340 per square meter).
a nine-month duration would be necessary for concurrent Categorizing the costs on the basis of the composition of a
construction of the concrete frames and in-filling of the modules module, the highest costs were found to be associated with floor
at the job site. However, the plan was changed to completing the panel and bathroom unit manufacturing, which accounted for
overall frames on site first and then commencing the in-filling 27.3% of the unit cost of a module, followed by 21.4% for
operation. This change was made to ensure a higher degree of furniture production and installation, 12.1% for finishes and
safety, considering that the project was the first application of the window installation, 10% for electricity, 8.8% for wall and
in-fill method in Korea. In addition, the construction was halted ceiling panel installation, 8.6% for electrical appliances, 5% for
from time to time because of delays in supplying the modules transportation, and 3.8% for plumbing fixture installation.
from the factory and coordinating the availability of a sufficient Based on the total construction cost of the pilot project and the
number of workers for construction of the reinforced concrete total area (3,700 m2), it is estimated that the net construction cost
structures. was $1,355 per square meter. However because this cost included
Based on the drawing shown in Fig. 4, the project management furniture such as desks, dining tables, beds, and electrical appliances
team planned that 11 modules would be installed on each floor. such as microwaves and refrigerators, if the costs of these items
On the fourth floor, which is the first floor on which the modules are deducted from the net construction cost, the total cost of the
were to be installed, four days were spent installing the 11 project was $4,608,500, or $1,245/ m2.
modules at a rate of two to three modules per day. For the fifth
through seventh floors, seven modules were lifted and six were 4. Applicability of the In-fill Method
installed per day resulting in a three-day duration. Regarding the
eighth and ninth floors, two days were spent due to lifting nine Table 2 summarizes the issues that arose in previous low-rise
modules and installing seven of them per day. For the tenth floor, modular projects in Korea, which can be considered problems
two days were also needed lifting 11 modules and installing nine that need to be managed successfully to ensure the quality of
per day. As the number of installations increased, the skill of the modular construction (Lee et al., 2012). Table 2 was used in this
workers in executing the installation processes was advanced. study as a framework for evaluating the modular in-fill method
During the schedule planning stage, the project management with respect to whether the same issues arose, whether any new
team considered the distance from the factory to the job site. issues arose, and whether the issues were addressed or mitigated
Because it took approximately 20 minutes to get to the job site by using the in-fill method.
from the factory and a 10-ton truck could transport one modular To perform the evaluation, a series of workshops were hosted
unit at a time, the ideal number of modules to be transported by with ten professionals: three engineers in involved in the pilot
one truck in a day was judged to be approximately six to seven, project, three construction management officials involved in the
considering the loading and unloading times per module in the public–private partnership program related to the pilot project,
factory and at the job site. Given an average of 40 minutes two research fellows in the Department of Modular Design in the
required to lift one module at the job site, it was estimated that a Korean Land & Housing Public Corporation, and the authors of
maximum of 12 modules could be lifted in a day. the study. The workshops were conducted three times as design
and construction quality control supervisions of the pilot project.
3.5 Construction Cost Analysis The following five subjects were discussed in the workshops: (1)
Table 1 summarizes the costs associated with the pilot project. the improvement of the issues listed in Table 2 achieved by
Item (1) reflects the net construction cost of the reinforced concrete applying the in-fill method, (2) noise-proofing measures, (3) fire
structures and Mechanical, Electrical, and Plumbing (MEP) resistance performance, (4) construction duration, and (5)
operations, excluding the module in-fill construction cost. The construction cost savings.

4.1 Improvements of the Issues

Table 1. Construction Cost Analysis of Case Project The issues listed in Table 2 are arranged in the order of the
Description Net cost ($) sequence of steps in the modular construction process, i.e.,
Construction 2,605,208 module production at the factory, module transportation to on-
Reinforced Concrete Electricity 272,000
Frame Work and Finish
site, on-site module lifting, and on-site construction, which
(excluding modules) Equipment 498,000 includes the structure, finish, and MEP. The “Improve” column
Sub total (1) 3,394,236 in Table 2 indicates whether each issue was addressed in an
Manufacture 1,344,883 improved manner by applying the in-fill method. An “O”
Modules On-site installation 272,892 indicates that an issue was resolved or mitigated, an “X”
Sub total (2) 1,617,775 indicates that the same issue arose even with the in-fill method,
Grand Total (3) 5,012,010 and “N.A.” (not applicable) indicates that an issue was not

− 1206 − KSCE Journal of Civil Engineering

 Unit Modular In-Fill Construction Method for High-Rise Buildings

Table 2. Issues in Previous Projects and Their Improvement

Process Issues Improve
1 Rework due to incomplete assembly drawings and specifications of module components O
Modules Factory
2 Re-manufacturing due to lack of company-wide standardization in modular components and materials O
Production
3 Rework due to low-level interface management during design, manufacturing, and installation O
4 Rework due to module deformation during transportation X
5 Contamination of internal/external finishes in ceilings and walls due to careless handling of modules X
Modules Transportation Delay due to difficult delivery conditions of modules caused by careless consideration of road conditions and
6 to Onsite N.A.
module size
Long waiting of transportation vehicle due to delivery of modules without consideration of proper onsite
7 N.A.
assembly priority of the modules
8 Onsite Module Lifting Damages on internal and external finishes due to torsion and deformation of the modules X
9 Onsite Construction Rework during module assembly due to deformation of modules O
10 (Structure) Difficulty of column-beam joints fabrication N.A.
11 During the finish process, increased manual works on-site and waste of materials due to lack of standardization O
Onsite Construction
12 Damages on the wall finish due to the interference between interior or exterior finish and MEP installation O
(Architectural Finish)
13 Rework due to incomplete architectural drawings and installation guidelines O
14 Rework of floor level/gradient due to a leak during the wet construction in water facility work O
Additional work such as box repositioning due to discrepancies between construction drawings / structural
15 X
drawings / mechanical drawings
Onsite Construction
Additional ceiling installation and steel frame reinforcement works due to not securing space for floor
16 (Mechanical/Electrical/ O
plate and ceiling facility plumbing
Plumbing)
Delay of construction schedule due to interference between water, sewage, electricity, fire resistant which
17 O
occurred simultaneously on-site
18 Increase of on-site works due to undefined components manufacturing needs O

relevant to the analysis. the in-fill method as originally introduced, a module and its
With respect to issues 1, 2, 3, 11, 12, 13, 14, 17, and 18 in related MEP components are designed and manufactured as a
Table 2, the workshop members discussed the fact that the issues unit and built on site by the firm. After inserting the modules in
arose mainly because of deficient interface management in the reinforced concrete structures, specialized MEP subcontractors
design, manufacturing, and on-site installation processes, as well simply connect individual modules with the main streams of the
as the immaturity of the modular technology. Currently, there are MEP in a building, thereby enhancing interface management
four modular construction firms in Korea, all of which focus on quality. This project procurement formation is beneficial in
load-bearing unit modules for low-rise buildings, as shown in mitigating problems related to miscommunication and interface
Fig. 1. mismatches, such as issues 1, 2, 3, 11, 12, 13, 17, and 18.
While they have company-wide drawings and specifications, Issue 9 and 16 were problems that arose because of the
those do not address overall design and construction of modules characteristics of the load-bearing module stacking method. Because
in conjunction with MEP but rather focus only on architectural the in-filling method utilizes a combination of conventional
panels and their connections. The MEP portions of a modular project structures and modular technology, these are not considered to be
are designed and built separately by specialized subcontractors. problems that need to be addressed.
In addition, there are no standardized industry-wide specifications
or detailed drawings for modular construction that integrate the 4.2 Floor Impact Noise Control
architectural portions with the MEP portions of a project. Modular There are three aspects of building performance and safety that
consumers are therefore not currently able to purchase standardized need to be satisfied in modular construction: floor impact noise
high-quality modular construction in the marketplace. control between floors, fire resistance, and structural stability
Issues 4, 5, 8, and 15 were not resolved using the in-fill (Lee et al., 2014). Since the in-fill method combines reinforced
method. These issues require careful planning in construction concrete structures with individual modular units, the overall
management. In the case project, there were several modules for structural stability of the building is maintained through the rigid
which the bathroom and bathtub tiles fell off because of vibration reinforced concrete structure.
during the module lifting and transportation processes. During Regardless of whether conventional or modular construction is
the discussion in the workshop, it was suggested that bathroom used, a significant concern in residential high-rise buildings is
tiles be finished on site using wet construction methods after the noise pollution induced by floor impact sounds such as footsteps,
modules are installed. falling objects, moving furniture, and chair dragging. In reinforced
As mentioned previously, the in-fill method was introduced in concrete buildings in particular, floor impact sounds from the
2011 by a multi-national cruise ship development EPC firm. In floor above are easily transferred to the floor below.

Vol. 20, No. 4 / May 2016 − 1207 −

 Hyung Keun Park and Jong-Ho Ock

To measure the noise level caused by floor impact sound Modular construction meets these criteria using fire-resistant
pressure in the pilot project, the project management performed panels. Because the in-fill method is based on construction of a
floor impact sound tests in accordance with the internationally reinforced concrete structure, which is fireproof, it is not
accepted test method ISO 140-7 (1998), “Field measurements of necessary to consider a floor requirement, but it is necessary to
impact sound insulation of floors” (Warnock, 1999). The test measure the fire resistance of the wall panels. The project
method consists of measuring sound pressure levels produced (a) management conducted laboratory tests to measure the fire
with a tapping machine to represent a lightweight impact source, resistance capacity of various wall panels. The tests were conducted
e.g., a person walking or pulling a chair on the floor above, and in accordance with the ASTM E-119 (1983) standard test
(b) using a bang machine to represent a heavyweight impact method for fire testing of building construction and materials.
source, such as a person running or a heavy object falling on the The test results showed that when the wall panel thickness was
upper floor. The sound pressure levels produced by the two types 100 mm, the one-hour requirement was satisfied, and when the
of sounds are measured on the lower floor with a sound level thickness was 125 mm, the two-hour requirement was satisfied.
meter.
The results of the measurements were averaged depending on 4.4 Construction Duration
the frequency and showed that the heavyweight impact noise On-site building activities using modular techniques are expected
was in the range of 22-27 dB and that the lightweight impact to have shorter construction durations and require fewer daily
noise was in the range of 27-34 dB. These ranges are much lower on-site workers and truck trips than conventional construction
than the limits set in various national noise standards, such as the techniques and therefore be less disruptive overall. To analyze
Korean standard (KSF 2810-2, 2012), the Japanese standard (JIS the degree to which construction durations were reduced using
A 1428-2, 2000), and the United States standard (HUD, 2014) the in-fill method, the three construction management professionals
(Jeon and Jeong, 2002). For example, according to KSF 2810-2, who participated in the workshop for the pilot project were asked
in first-grade buildings, the floor impact sound pressure of a to estimate the construction duration for a building of the same
lightweight impact noise should be below 43 dB and that of a size as the pilot project using conventional construction techniques.
heavyweight impact noise should be below 40 dB. Similarly, JIS The responses varied depending on the experience of individuals
A 1428-2 indicates that for first-grade buildings, the floor impact but ranged from 12 to 13 months in the case of a reinforced
sound pressures for lightweight and heavyweight impact noises concrete frame and from 10 to 11 months in the case of a steel
should be below 45 dB and 50 dB, respectively. The results of frame. Comparing the numbers with the initial estimate of the
the analysis show that the in-filled method is effective in pilot project duration, nine months, the in-fill method appears to
reducing floor impact noises. The reason for this is that a module provide a time-saving feature. However, given that the actual
is placed on a reinforced concrete slab, and the concrete slab and duration of the pilot project was 10 months, which included one
the ceiling and floor panels of the module create an effect similar month in addition to the initial estimate because of field safety
to a floating floor, which is a construction technology that is concerns and module supply and worker procurement delays, the
widely used to mitigate floor impact noise in residential buildings in-fill method was not judged to be superior to conventional
(Warnock, 1999). In addition, the space between the modular construction in terms of minimizing the construction duration.
ceiling panel and the upper concrete slab of each floor acts as an Therefore, to achieve a time savings benefit with the in-fill method
air buffer zone to prevent noise from being transferred. in comparison to conventional construction, it is necessary to
conduct further research on interface management improvements.
4.3 Fire Resistance Performance
The performance of walls, floors, and other building members 4.5 Construction Cost Savings
under fire exposure conditions is a matter of major importance in The pilot project was compared with other building projects to
ensuring that buildings do not jeopardize the safety of neighboring assess the cost-saving features of the in-fill method. The comparison
structures or the public. In residential buildings, each dwelling was conducted using 2012-2013 construction cost data for 186
usually forms a separate fire compartment of walls and floors public projects provided by the Korean Public Procurement
that ensure fire resistance for some minimum time period. Service (KPPS, 2014).
The Korean national building code defines the minimum fire The use of public-sector cost data rather than private-sector
resistance time period for walls and floors, depending on the data was expected to permit relatively consistent cost comparisons
building type, such as residential or business, the number of on the basis of government budget-based contract histories.
building floors, and the building height. For example, in the case Taking into consideration differences in the exterior and interior
of a residential building with less than 12 floors and a maximum finish materials of public buildings, the construction cost distributions
height of 50 m, both the load-bearing exterior walls and the were in the ranges of $1,150/m2 to $1,350/m2 for reinforced
interior walls must have two-hour fire resistance, whereas curtain concrete structures and $1,400/m2 to $1,600/m2 for steel
walls, whether exterior or interior, must have one-hour fire structures. As mentioned earlier, the unit cost of the pilot project
resistance, and floors must have two-hour fire resistance (Lee et was $1,245/m.2
al., 2014). Although the in-fill method thus appears to achieve a slight

− 1208 − KSCE Journal of Civil Engineering

 Unit Modular In-Fill Construction Method for High-Rise Buildings

cost savings, if the higher labor costs associated with conventional two have been used since 2005. The third, so-called CHS, was
construction projects are considered, a greater benefit in cost introduced in 2011 by a multi-national cruise ship development
savings is expected to be achievable. A recent study showed that EPC firm.
the ratio between material costs and labor costs in conventional Although CHS has recently been employed in the construction
construction projects ranges from 50:50 to 37:63 and that labor of several high-rise dormitories in Korea, there is very little
costs are expected to increase further, accounting for up to 70% information regarding its application to high-rise buildings. A
of total project costs, because of the shortage of experienced 12-story residential building that was recently constructed with
workers. (Korea Appraisal Board, 2013). The factory production CHS was used as a pilot project. The main objective of this study
environment of modular construction mitigates the labor- was to assess the applicability of CHS from construction cost
intensiveness of conventional construction. and scheduling points of view by performing a case study of the
One more prospective benefit of the in-fill method that needs pilot project. The benefits of the in-fill method were identified by
to be further studied in examining its cost effectiveness is the evaluating the improvements achieved with respect to issues that
economy of various aspects of the structural design. The average have arisen in previous modular construction projects in Korea.
floor height of a reinforced concrete building in Korea is in the The pilot study building is a 12-story apartment building with
range of 3.6 to 4.5 m, depending on the complexity of the one basement floor, 12 superstructure floors, and a total floor
building. However, in a modular building, the floor height can be area of 3,700 m2. The frames of the building consisted of
reduced by up to 3 m because a ceiling is not necessary and MEP reinforced concrete structures. The first through third floors are
pipes are not installed in the ceiling. occupied by shops, and the fourth through tenth floors are studio
The in-fill method combines conventional reinforced concrete apartments with in-filled unit-modules. To assess the improvements
structures with modular construction, so the overall cost- achieved with respect to the issues identified, three workshops
effectiveness of the method depends on the modular portion of a were hosted with ten professionals. The main findings and
project. In addition, because the modules are manufactured in a results of the discussions in the workshops are summarized as
factory, their cost effectiveness depends on the total number of follows.
units manufactured in the factory. As more units are manufactured, The issues that arose in previous low-rise modular projects
the production cost of a modular unit becomes more economical. were due mainly to deficient interface management in the design,
manufacturing, and on-site installation of the modules and the
5. Research Limit immaturity of the modular technology. There are no standardized
industry-wide specifications or drawings for modular construction
As stated earlier, Table 2 summarizes the issues in previous that integrate the architectural and MEP portions of the project.
low-rise modular projects that need to be managed successfully Modular consumers are thus not able to purchase both standardized
to ensure the quality of modular construction. While it is and high-quality modular construction in the marketplace.
desirable to numerically represent the improvement level of the From a construction duration perspective, for the in-fill method
issues by means of the in-fill method, this study simply presented to be beneficial in comparison to conventional methods, it is
whether those were improved or not in the case project. necessary to conduct further research on interface management
Although the CHS technique has been applied to a 12-story and improvements. The construction of the pilot building required a
a 16-story hotels in China, there is very little information total of 10 months. Estimates of 12-13 months and 10-11 months
available concerning the usability of the method in improving were obtained for reinforced concrete and steel frames,
the issues. respectively. However, given that the actual duration of the pilot
As more projects with the in-fill method are to be implemented project was 10 months, the in-fill method was not clearly superior
in the future, it is expected that more reliable analysis as to the to conventional construction in minimizing the construction
applicability of the in-fill method to enhance modular construction duration.
quality can be implemented. The pilot project was compared with other buildings to assess
the cost-saving advantage of the in-fill method. Taking into
6. Conclusions consideration the differences in the exterior and interior finish
materials of public buildings, the construction cost distributions
In modular construction, 80 to 90% of the modules are were in the ranges of $1,150/m2 to $1,350/m2 for reinforced
manufactured in a factory, transported to a job site, and assembled concrete structures and $1,400/m2 to $1,600/m2 for steel structures.
on site to form a building structure. In spite of its widespread The unit cost of the pilot project was $1,245/m2. Although the in-
application to low-rise buildings over the last 30 years, modular fill method was slightly more cost effective, if increases in labor
construction is a relatively new approach to high-rise building costs associated with conventional construction projects are
construction. considered, the in-fill method appears more economical.
Three modular construction methods have been used to build The results of noise pressure level measurements showed the
high-rise buildings: the core method, the core-and-podium heavyweight impact noise was in the range of 22-27 dB and that
combination method, and the modular in-fill method. The first the lightweight impact noise was in the range of 27-34 dB. These

Vol. 20, No. 4 / May 2016 − 1209 −

 Hyung Keun Park and Jong-Ho Ock

ranges are much lower than the limits set in various national buildings.” Structures and Buildings 163 Issue SB3, Proceedings of
noise standards. the Institute of Civil Engineers, pp. 151-164.
According to the laboratory tests to measure the fire resistance Lawson, R. M., Ogden, R. G., Pedreschi, R., and Popo Ola, S. O. (2005).
“Prefabricated systems in housing using light steel and modular
capacity of the wall panels in the pilot project, when the wall
construction.” Steel Structures, No. 5, Korean Society of Steel
panel thickness was 100 mm, the one-hour requirement was Construction, pp. 477-483.
satisfied, and when the thickness was 125 mm, the two-hour Lawson, R. M., Ogden, R. G., and Bergin, R. (2012). “Application of
requirement was satisfied. modular construction in High-rise Buildings.” Journal of Architectural
Engineering, No. 18, ASCE, pp. 148-154, DOI: 10.1061/(ASCE)AE.
Acknowledgements 1943-5568.0000057.
Lee, J. Y., Kim, J., Chang, H. J., and Kim, J. M. (2014). “Long-term
This research was supported by a grant from the Seoul structural behavior of resilient materials for reduction of floor impact
sound.” International Journal of Civil, Architectural, Structural, and
National University of Science and Technology, Seoul, Korea.
Construction Engineering, Vol. 8, No. 5, pp. 509-512.
Lee, Y. H., Lee, D. H., and Kim, K. T. (2012). “Considerations in the
References early stage of designing the unit modular building.” Journal of
Korean Institute of Construction Engineering and Management,
Azari, R., Javanifard, N., Markert, D., Strobei, K., and Yap, J. (2013). Vol. 13, No. 6, KICEM, pp. 133-141.
Modular fabricated residential construction – constraints and Lee. D. H. and Ock, J. H. (2014). “A study on the application of the in-
opportunities, PNCCRE Technical Report #TR002, University of fill construction method to high-rise unit modular buildings.” Journal
Washington, pp. 57-60. of Architectural Institute of Korea, Vol. 30, No. 3, pp. 105-114.
Cartz, J. P. and Crosby, M. (2007). “Building high-rise modular homes.” Lu, N. and Korman, T. (2010). “Implementation of Building Information
The structural Engineer, Vol. 85, No. 19, pp. 20-21. Modeling (BIM) in modular construction: Benefits and challenges.”
Cho, B. H. (2011). “A study on unit modular design method of urban- Construction Research Congress 2010, ASCE, pp. 1136-1144.
type housing.” Journal of the Korean Housing Association, Vol. 22, STACO (2011). Cruise Housing System with STACO Modular System,
No. 5, KHA, pp. 101-110. STACO Construction Inc.
Jeon, J. Y. and Jeong, J. H. (2002). “Objective and subjective evaluation Warnock, A. C. C. (1999). “Controlling the transmission of impact sound
of floor impact noise.” Journal of Temporal Design in Architecture through floors.” Construction Technology Update No. 35, Institute
and the Environment, Vol. 2, No. 1, pp. 20-28. for Research in Construction, National Research Council of Canada,
Korea Appraisal Board (2013). The unit construction cost data book for pp. 1-6.
the evaluation of property. Yu, I. H. and Park, S. K. (2011). “Vitalization of pre-fabricated buildings
Korean Public Procurement Service (2014). The 2012-2013 construction to enhance competitiveness of specialty construction business.” Korean
cost data book. Research Institute for Construction Policy, pp. 33-45.
Lawson, R. M. and Richards, J. (2010). “Modular design for high-rise

− 1210 − KSCE Journal of Civil Engineering