This document summarizes the design of a six-story office building with a hybrid lateral force resisting system. The building uses concrete shear walls in the north-south direction and both shear walls and special moment resisting frames in the east-west direction. Gravity columns, beams, and their connections were designed to only carry vertical loads. The moment frames were designed to resist 25% of the base shear from seismic loads. Reinforced concrete shear walls were also designed to resist seismic loads. The document provides details on the modeling, analysis, design of the various structural components, and conclusions on the efficiency of the hybrid lateral force resisting system.

1. Six Story Office Building: Hybrid LFR
System Design
Building Design Group Project
May 5, 2016
CE 448/548 – Building Design
Team #4:
Abhishek Jain, Mahmoud Faytarouni, Nate Scharenbrock, and Phil Iekel

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Table of Contents
Table of Contents.........................................................................................................................................i
Summary of Figures ....................................................................................................................................i
Summary of Tables......................................................................................................................................i
Introduction: ...............................................................................................................................................1
Model and Loading:....................................................................................................................................2
Design of Gravity Frame and Connections: .............................................................................................5
Design of Moment Frame and Connections: ............................................................................................7
Design of Shear Wall: .................................................................................................................................9
Conclusions: ..............................................................................................................................................10
Appendices: ...............................................................................................................................................11
Summary of Figures
Figure 1. Plan view of building with LFR systems highlighted ................................................................... 1
Figure 2. Concentrated dead loads on the frame (kips) ................................................................................ 2
Figure 3. Distributed loads on the frame (kip/ft) ......................................................................................... 3
Figure 4. Equivalent Lateral Forces acting on shear wall in East-West direction ....................................... 4
Figure 5. Equivalent Lateral Forces acting on the moment frame in the East-West direction ..................... 4
Figure 6. Equivalent Lateral Forces acting in the North-South direction on the shear wall ........................ 4
Figure 7. Gravity columns ........................................................................................................................... 5
Figure 8. Plan view of the gravity beams; .................................................................................................... 6
Figure 9. 3D Rendering of shear connection. .............................................................................................. 7
Figure 10. Deflected shape of moment frame. ............................................................................................. 8
Figure 11. 3D rendering of a typical moment connection ............................................................................ 8
Summary of Tables
Table 1. Gravity column schedule. ............................................................................................................... 5
Table 2. Schedule for moment frame member sizes. ................................................................................... 7

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Introduction:
Composite/hybrid structures have been increasingly popular in buildings for the last two decades. In fact, more
buildings used composite structures than any other structural system, based on floor areas. Composite systems are
also known as dual systems and are very safe and efficient in dissipating energy from an earthquake. Dual systems
have various advantages: they increase the ductility of the system and are generally more economical because they
limit the number of moment connections. In a dual system, the stiffness of shear wall is used to control drift, which
prevents the need for large members in the moment frame. The most important benefit is that there are a large
number of redundancies in the system, which prevents failure of the whole structure when a local failure occurs.
In this report, the design of dual system has been shown along with the drawings of beams, columns and
connections. All design checks were performed according to the design codes to ensure adequate strength.
This report also includes the structural detailing of all beams and columns for the building. The software used for
drawings and analysis include: Autodesk Revit, AutoCAD, Autodesk Advance Steel and SAP 2000.
Background:
The proposed building was a six story office building measuring 75 feet in height. The building has reinforced
concrete shear walls in North-South direction and both shear walls and special moment resisting frames in East-
West direction, as seen in Figure 1. Beams and columns not part of the moment frame were designed to only carry
gravity load. For the efficient design, we have assumed that the concrete deck creates a rigid diaphragm which
causes the building to deform uniformly as one body.
The codes that were used for this design project include: ASCE 7-10, ACI 318-11, AISC 341-10, AISC 358-10 and
AISC 360-10. The LRFD method was used because it proves efficient for design for lateral load. The site is
located in the Midwest where SS=0.4, S1=0.2 and TL =12 sec. Dead load, which includes member self-weight,
was taken as 90 psf. The live load at each floor level was considered to be 50 psf. The snow load on the roof was
taken as 30 psf. As per the data provided, wind load was taken as 30 psf. Seismic design and detailing was taken
into consideration for all members of the dual system. The controlling design combination used
was ((1.2+0.5SDS)D.L.+1.0L.L.+0.2S.L.+QE.
Figure 1. Plan view of building with LFR systems highlighted

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Model and Loading:
Loading information was given in the project statement, as detailed above. A single moment frame was analyzed in
SAP-2000 out of plane dead and live gravity loads were combined into point loads acting on the columns.
Distributed loads were applied to the beams and were based on tributary area. Figures 2 and 3 (shown below)
represent the loads induced all gravity loads. Note that the roof loads are smaller than the other floors due to the
fact that the snow load replaces the larger live load on the roof for the load combination. Loading on the exterior
moment frame columns was also larger than the interior ones due to distributed load on the two gravity bays.
Figure 2. Concentrated dead loads on the frame (kips)

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Figure 3. Distributed loads on the frame (kip/ft)
Both wind and seismic lateral loadings were analyzed to determine which load case would govern. Both load cases
were distributed to the moment frames and shear walls based on stiffness. To obtain reasonable lateral loads for
seismic design, the equivalent lateral force (ELF) method was used. Seismic was determined to control, and the
comparisons along with all other load calculations can be found in Appendix B. Below are pictorial summaries of
each of the ELF distributions on the frames, with the first two oriented in the East-West direction and the third
providing lateral stability in the North-South direction. For the dual system the moment frame was designed to take
25% (or 12.5%/frame) of the total base shear determined. AISC specifies this to provide appropriate ductility
behavior in the event that the shear wall enters the inelastic zone.
Once loading calculations were completed, load cases were designated in SAP-2000 to perform a complete analysis
of the structure using the preliminary sections.

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Figure 4. Equivalent Lateral Forces acting on shear wall in East-West direction
Figure 5. Equivalent Lateral Forces acting on the moment frame in the East-West direction
Figure 6. Equivalent Lateral Forces acting in the North-South direction on the shear wall

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Design of Gravity Frame and Connections:
Gravity frame calculations were performed in MathCAD and then checked with the analysis in SAP-2000. All
calculations can be found in Appendix C. As shown in Figure 7, due to the geometry of the building there are
gravity columns on the exterior (bays that are not part of the LFR systems) as well as the interior bays. By
definition gravity columns experience purely axial compressive force generated by the loads above and are not
designed to take any bending moment induced by the lateral forces. The edge columns were designed separately
from the interior columns enabling a smaller member size and more efficient design.
Member sizes were selected considering both uniformity and constructability. Column sizes were changed every
two floors, with column splices 4 feet above the floor. This design benefits from being somewhat redundant, but
still remains efficient and not overdesigned (as the structure would be if the same section sizes were used along all
frames). W12 sections were chosen based off of floors 1, 3, and 5 loading. As noted in Table 1, edge column sizes
were also smaller due to a decreased tributary area.
Figure 7. Gravity columns
Table 1. Gravity column schedule.
For beam design it was assumed that the axial force on the beams was equal to zero. Because the 3.5” concrete
metal deck overlays the substructure, the steel beams were designed as composite sections with the deck, and
incorporated 3” metal studs spaced at 18” along the beams. Loading was the same for all floors, so beam loading
was analyzed from Line E and Line 5 and then projected out to the rest of the structure. Figure 8 shows the beam
layout. In the North-South direction gravity beams (blue) exist in all bays except for the shear wall bay in the

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middle. Bending capacities were checked, and the smallest W21 section available was selected. In the East-West
direction the beams (green) occupy all bays except for the highlighted red portion, which are the moment frames.
Figure 8. Plan view of the gravity beams;
W21x44 are green in E-W direction, W21x50 are in blue in the N-S direction, red is the moment frame.
Gravity frame design is not possible without having the right member connections. For ease of constructability in
the field and cost efficiency it was a goal to have as many shear connections as possible. The shear connection used
on all floors was similar, a single angle bracket L3 1/2 “ x 3 ½” x 5/16” was used. In the North-South direction a 9
inch angle was used with three bolts. In the East-West direction a 12 inch angle and four bolts were used. A 3D
rendering of this connection can be seen in Figure 9 below. Several different limit states were checked to ensure
adequacy of the connection including:
 Bolt Shear Capacity
 Bearing Strength
 Shear Yielding
 Shear Rupture
 Block Shear
Calculations for the shear connection design can be found at the end of Appendix C, with detailed drawings in
Appendix A.

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Figure 9. 3D Rendering of shear connection.
Design of Moment Frame and Connections:
Steel moment resisting frames provide adequate strength to resist seismic demand forces. Steel moment frames can
have an adequate stiffness to limit the story drift and to develop plastic hinges at the end of the beams.
As discussed above, ACI 318-14 addressed, a minimum of 25% of the lateral loads should be resisted by the
moment frames in case of dual system. The reason of that is when the shear walls or the core walls start to crack,
where a reduction in the flexural stiffness will occur, the moment frames will accommodate for this reduction.
The moment resisting frame system in the East-West direction had two moment resisting frames. The frames
consisted of four columns on grid A and F. The columns were 30 feet on center. All the columns on the moment
resisting frames were oriented with their strong axes in the plane of the frame. The location of the moment resisting
frames were carefully studied in order to minimize the torsional effects.
Also, there were steel gravity columns as mentioned above intended to resist only gravity loads because they were
not part of the lateral load resisting systems. SAP-2000 was used to analyze the frames in this project. The analysis
that was considered in modeling the associated frames was linear static analysis.
A procedure was followed in order to get the most economical system while still adhering to the safety codes. The
beam sizes were increased as the floor number increases. The strength of the members were sufficiently designed to
10- 20 % to meet Strong Column-Weak beam requirements. In addition to that, another controlling factor was the
story drift ratio. The final section sizes can be seen in Table 2. Additionally, the deformed shape can be seen in
Figure 10. All of the calculations for the moment frame can be found in Appendix D.
Table 2. Schedule for moment frame member sizes.

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Figure 10. Deflected shape of moment frame.
The moment connection design was perfromed considering reduced beam section (RBS). This design helped to
ensure the plastic hinge would form in the beam. Additionally, continuity plates were required to be placed in the
column. The detail can be found in Appendix A and the caluclations in Appendix D. Below is a 3D rendering of a
typical moment connection.
Figure 11. 3D rendering of a typical moment connection

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Design of Shear Wall:
Lateral forces acting on buildings such as wind forces or/and seismic forces, can be resisted by different means.
Many lateral force resisting systems were presented in the current provisions or even in the old provisions. One of
the lateral resisting systems that is used, especially when a heavy lateral forces are likely to occur from an
earthquake, is the reinforced concrete shear wall. Shear walls or core walls (shear reinforced concrete walls
enclosing stairways or elevator shafts) can be included to resist solely the lateral forces or even part of the
gravitational loading.
There are several considerations should be taken into account in designing a shear structural wall. Some of these
considerations that have been examined in this project are having enough rigidity, sufficient vertical load, desirable
location of the shear walls, adequate shear strength, and sufficient thickness. In order for the building to resist the
service loads without excessive vibrations or deflections, enough ductility should be achieved. The reinforced
concrete shear wall has to be loaded with a sufficient vertical loads in order to resist the uplift induced by the
foundations of the walls due to lateral loads. The location of the shear walls with or without a structural steel frames
should be carefully studied to minimize the torsional deformations of the building. The reinforced concrete walls
should be designed to have a sufficient strength to resist shear, flexure, and axial loads. Lastly, the fire code
requirements should be checked since it might govern the wall thickness and cover of the reinforcement.
In this project, the lateral load resisting system used in the North-South direction consisted of reinforced concrete
shear walls 15 inches thick and a maximum of 26.5 feet in length. The lateral load resisting system used in the East-
West direction consisted of reinforced concrete shear walls and steel moment resisting frames. The reinforced
concrete shear walls were 16 inches in thickness and with a maximum of 10.5 feet in length for each one. The shear
walls were assumed and designed separately from each other, so the combined effect of the shear walls in design
was ignored. In other words, the shear walls were not designed as if having two core walls, thus making the design
conservative. The shear walls were designed based on the special seismic provisions, in which the benefit of the
boundary element was utilized. All the boundary element requirements and checks were applied and satisfied. As a
result of that, the percentage of the steel reinforcement at each end of the shear wall was much higher than the
percentage of the steel reinforcement distributed in the middle. Moreover, and for detailing purposes, the
reinforcement of the shear walls were detailed following the detailing of a regular core wall.

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Conclusions:
The six story dual LFR building was designed with efficiency and cost savings in mind, while also maintaining an
appropriate level of safety. In building design the lateral resisting systems are often the most expensive part of the
building structure. Because of this it was a goal of the design team to take advantage of and utilize gravity columns
and beams wherever possible, thus decreasing the section sizes in these areas. With lateral resisting systems
relegated to one bay in the North-South direction (Line 1 and 6) and three bays in East-West direction (Line A and
F), the impact of the systems, both aesthetically and economically, is minimized. Within the dual system, increased
ductility of moment frame and the stiffness of the shear wall provided a reduction in member sizes. Torsional
effects can also be neglected due to the placement of the LFR systems on the exterior of the building.
The scope of this project covers many of the design components included in a typical building. It should be noted,
however, that there are several critical sections that need attention before final design drawings can be submitted
for construction. These include cladding design, base plate connection design and foundation requirements, and
column splices. While important to the project, these design considerations are not critical to the overall design of
the building (meaning the building layout and member design is unaffected by the addition of each of these
components). The design team feels confident that after attention to these finer details the documents are ready to
be turned in for final review and then construction.

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Appendices:
 Appendix A: Drawings
 Appendix B: Lateral Loading Calculations
 Appendix C: Gravity Frame Design Calculations
 Appendix D: Moment Frame Design Calculations
 Appendix E: Shear Wall Design Calculations