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Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 7
STRUCTURAL
The structural system of the James C. Renick School of Education Building is split into two
sections. However, the two sections do not follow the same scheme as the two architectural
“bars”. The split allows for the cantilever to disengage from the rest of the building. Using an
expansion joint, the Renick building technically becomes two separate structures during
design analysis. The cantilever section, which is the focus of this report, will be referred to as
the northern wing, while the rest of the building is the southern wing1.
Stewart Engineering, Inc. located in Charlotte, North Carolina, completed the structural
design. Using RAM Structural and RISA 3-D for computer analysis, the structural system was
determined to be adequate for the design loads located within ASCE 7-98. The Renick
Building must follow the North Carolina State Building Code, a form of the 2000 International
Building Code (IBC). When completing the computer investigations, the structural system was
examined using both design methods, the load resistance factor design (LRFD) and the
allowable stress design (ASD). Under careful consideration, it was determined that seismic
loads contributed to larger forces on the building than wind loads. For one thing, the Renick
Building is only three stories high. Also a factor is the nearby epicenter of a disastrous
earthquake during the late 1800s, Charleston, South Carolina. For this reason, it was a
challenge to provide substantial strength, especially for the cantilever, under many load
combinations.
The structural system includes several features. The huge cantilever trusses located in
the north building have diagonal wide flange bracing members that carry forces from both
gravity and lateral loads, and help to distribute them into wide flange girders and columns
that are designed to resist moments and bear axial compression. Diagonally placed HSS
rectangular tubing is used in both vertical and horizontal directions to provide bracing against
lateral loads without adding too much weight to the structure. Two shear walls at the base of
the cantilever carry gravity loads from the overhang, yet also stabilize the cantilever from
lateral vibration and help to dissipate loads down to the foundation and soil below. A
concrete slab on composite metal decking works together with shear studs that are welded to
the floor-supporting steel beams, creating a stronger floor system and ultimately reducing slab
thickness and beam sizes. A shallow foundation system carries the total building loads while
saving money on the amount of concrete used during construction. 1 Enlarged Structural Plans for the North Wing located in Appendix C
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 8
Applicable Building Codes: • 2002 North Carolina State Building Code (2000 IBC with Revisions) • ACI 318-99 Requirements for Structural Concrete • ACI 530-99 Requirements for Masonry Structures • AISC Manual of Steel Construction, ASD, 9th Edition • AISC Manual of Steel Construction, LRFD, 3rd Edition • ASCE 7-98 Minimum Design Loads for Buildings • American Welding Society D1. 01-98 • SJI-92 Standard Specs, Load & Weight Tables for Steel Joists & Joist Girders
Materials:
• Structural Steel ASTM A992, Grade 50, Fy = 50 ksi HSS ASTM A500, Grade B, Fy = 46 ksi Miscellaneous Steel ASTM A36, Fy = 36 ksi Reinforcing Steel ASTM A615, Fy = 60 ksi
• Concrete - Lightweight f’c = 4000 psi (elevated slabs)
Normal weight f’c = 3000 psi (slab on grade, walls, footings)
• Bolts ASTM A325 – ¾” diameter
Load Combinations: Strength Design – ASCE 7-98 (sect 2.3.2, p.5) & IBC 2000 (sect 1605.2, p. 296)
• LRFD-1 1.4(D+F) • LRFD-2 1.2(D+F+T) + 1.6(L+H) + 0.5(Lr or S or R) • LRFD-3 1.2D + 1.6(Lr or S or R) + (0.5L or 0.8W) • LRFD-4 1.2D + 1.6W + 0.5L + 0.5(Lr or S or R) • LRFD-5 1.2D + 1.0E + 0.5L + 0.2S • LRFD-6 0.9D + 1.6W + 1.6H • LRFD-7 0.9D + 1.0E + 1.6H
Allowable Stress Design – ASCE 7-98 (sect 2.41, p.5) & IBC 2000 (sect 1605.3, p. 298)1 • ASD-1 D • ASD-2 D + L + F + H + T + (Lr or S or R) • ASD-3 D + L + (Lr or S or R) + (W or 0.7E) • ASD-4 0.6D + W + H • ASD-5 0.6D + 0.7E + H • ASD-6 D + L • ASD-7 D + L + S + E/1.4 • ASD-8 D + L + W • ASD-9 D + L + W + 0.5S • ASD-10 D + L + S + 0.5W • ASD-11 D + L + S + 0.71E • ASD-12 0.9D + 0.71E
1 ASD Method not accounted for in this report
D = Dead Loads S = Snow Loads H = Soil Loads # L = Live Loads W = Wind Loads F = Fluid Loads # Lr = Roof Live Loads E = Earthquake Loads R = Rain Loads #
T = Self-straining Force (temperature) # # - Not in the scope of this report
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 9
GRAVITY SYSTEM Design Loads:
• Dead Loads
1st Floor (psf) 4” Normal weight slab on grade 50.0 (4/12)ft*150pcf Floor Finish 1.0 From ASCE-07 51.0 TOTAL 2nd/3rd Floor Concrete slab on metal deck1 41.0 From USD Manual pg. 38 Suspended ceiling grid 2.0 From ASCE-07 5/8” Gypsum board panels 6.0 From ASCE-07 MEP 5.0 From ASCE-07 Floor Finish 1.0 From ASCE-07 55.0 TOTAL Roof Built-up roofing 2.0 From ASCE-07 ¾” Fiberboard 1.1 1.5 psf per 1” thickness 3” Rigid insulation 4.5 0.75 psf per ½” thickness Suspended ceiling grid 2.0 From ASCE-07 MEP 5.0 From ASCE-07 Concrete slab on metal deck2 31.0 From USD Manual pg. 38 45.6 TOTAL
• Live Loads
(psf) Roof 20 Classrooms 40 Live Load Reductions: Office 50 Applicable to floor live loads only. Office w/ Partitions 80 Not permitted where Live Load 100 psf. Upper Floor Halls 80 All columns minimal reduction = 20%. Public Areas, Lobby 100 If support area > 400 sq. ft., then reduce loads Ground Floor Halls 100 in beams, columns, walls, foundations Stairs 100 L = Lo(0.25+(15/SQRT(KLL*AT)) Storage 125 KLL=Live load element factor (Table 1607.9.1) Mechanical 150 AT= Tributary area
• Snow Loads
pf=0.7CeCtIpg Pg 17.0 psf Ce 1.0 Ct 1.0 I 1.1
pf 13.09 psf < 15.0 psf3 pf 15.0 psf
1 3¼” Light-weight concrete slab on 2”- 20 Gage composite metal deck 2 2” Light-weight concrete slab or 2” cellular concrete on 1½”- 22 Gage metal deck 3 Minimum per North Carolina based IBC Code
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 10
Typical North Building Structural Plan
The north building is a steel braced frame structure with two enormous two-story trusses
running parallel to each other1. The trusses actually resemble that of a cantilevered bridge’s
supporting members2. They work together with seven steel columns and a pair of 12” thick,
reinforced concrete shear walls to provide the bulk of the strength in the northern wing3.
The floor system, shown below, at the second and third levels, consists of a 3¼” thick,
4000 psi lightweight concrete slab on three-inch, 20-gage, Type-NS composite metal deck.
The decking spans north-south resting on 40’ long steel wide flange bbeeaammss44 that connect the
ggiirrddeerrss of the two cantilever trusses. These beams, spaced every ten feet on center, are
W21x50s, W21x44s, or W24x55s. Two rows of W14x34 jjooiissttss span perpendicular to the beams to
provide extra support for the slab decking. Two sshheeaarr wwaallllss form the central core to the
cantilever structure, and enclose a fire escape stairwell for that portion of the building.
The roof consists of two-inch, lightweight cellular concrete on 20-gage metal deck. It
slopes east or west, away from the cantilever’s centerline at ¼” per foot. The roof beams are
bent W21x44s, that follow the slope of the roof and are also spaced at ten feet on center.
The length of the cantilever is 52’-6”, requiring two hefty girders at each level to support
the floor weights and help distribute loads from the diagonal braces. The second floor and
1 See next page for Truss Elevation 2 See page 27 for Cantilever Bridges 3 Enlarged North Building Plans located in Appendix C 4 Colors represent members in typical plan, this page
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 11
_ Temporary Supports _
Cantilever Elevation
roof girders are W14x211s and the third floor girders are W14x90s. As specified by the
engineers, the cantilever trusses are to be constructed prior to shipping them to the site. Each
truss will be assembled in two pieces.
Piece 1, shown below, consists of the second and third floor girders along with the
second floor spliced columns and braces. Piece 2 will be built with only the roof girders to
connect the third floor columns and braces. The girders, or truss chords, are to be fabricated
in the steel plant at a length desirable to the fabricator. The engineers gave a suggestion for
the splice location of these girders, recommending lengths of 38’-1½”, 39’-11”, & 29’-1½” at
each floor level1. It was also recommended that each piece be disassembled into three
separate parts for easier transportation to the site.
None of the proposed chord lengths can cover the entire spread of the overhang on
their own, calling for a splice at some point along the unsupported length. To provide
adequate strength for a split requires sturdy shear splice connections2. In fact, these
connections were designed with 88 bolts, 72 of which bolt the two girders together with splice
plates located on both top and bottom of the wide flanges. Two shear plates, one on each
side of the girders’ webs, require the other 16 bolts to complete the connection.
When construction of the cantilever begins, the only parts shown above that will be
standing are the 17-foot high, ground floor columns. The girders are not spliced at the column
locations, so the entire truss will be bolted down with the use of ¾” cap plates at the top of
each column and stiffener plates located between the girder’s flanges2. This will result in a
substantial uplift force in the column on the far left once the truss pieces are in place. For this
1 Splice Locations found in Enlarged Truss Elevations on pages 19 & 20 2 Splice Connection Detail located in Appendix E
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 12
reason, two temporary supports are placed under the cantilever until the entire structure is
bolted in place. The two shoring members, to be supplied by the construction team, should
be capable of enduring at least 125 and 200 kips of axial load, respectively.
The columns that come preassembled at the second and third floor levels are also
bolted with base or cap plates to the flanges of the continuous girders. Except for the two
W14x132 columns at grid line 3, they are all W14x43s. Most of the vertical bracing members
are also W14x43s. Welded into the girders and bolted to the columns using panel-point
connections with various bolt assemblies, these braces deliver axial forces to the truss chord.
The bracing connections, in one way shape or form, involve a gusset plate that is welded at
full penetration to the girder and bolted to either double angles or double shear plates that
are welded to the column. The brace is then attached to the gusset plate by bolting splice
plates to the brace’s web and claw angles to the brace’s flanges1.
The steel columns at ground level are attached to the concrete footings with base
plates that range in size from a 1’-2” square, at one inch thick, to 1’-8”x1’-10”, two inches thick.
The base plates are all bolted with four A36 or A307 anchor bolts, one at each corner, located
two inches from the edges. Soil samples showed that a shallow foundation system would work
exceptionally well, resting on soil with a bearing pressure of 3000 psf; especially if the depth
does not go beyond a 24” footing thickness for frost protection reasons. The shallow footings
are made of 3000 psi, normal weight concrete and range in depth from 1’-6” to 2’-6”. A four-
inch deep slab on grade consists of 3000 psi, normal weight concrete and contains 6x6-
W2.1xW2.1 welded wire mesh reinforcement at 1½” down from the top of the slab. It shall rest
on top of a four-inch thick layer of compacted NCDOT #57 stone.
As listed in the subsurface exploration report, the allowable net bearing pressure can
actually be designed for up to 5000 psf, if the footings rest on hard residual material below 790
feet. This happens to coincide very well with the positioning of the columns that support the
huge cantilever loads. The building site slopes from a height of 813’ above sea level at the
southwest corner down to an elevation of 790’ on the northeast side, at the cantilever
columns. There are seven cylinder shaped caissons underneath these columns to help drive
the extreme point loads from the cantilever trusses well below the surface to solid rock. The
values of these vertical loads could reach as high as 1200 kips. The six-foot diameter caissons
are all to be approximately 12’ deep, depending on the depth of rock below ground level.
There is an issue concerning differential settlements in the building’s foundation due to the 1 See connection details in Appendix E
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 13
Typical South Building Structural Plan
combination of deep caissons and shallow footings. However, the soil below an elevation of
790’ was found to be a small layer of highly consistent residual soil on top of partially
weathered rock, so settlements should be limited. In fact, the soil report insists that the crucial
settlement will occur during construction and can be estimated to be less than ½”.
The south building is a steel frame structural system as well; however its layout is much
simpler than the north building. The floor slab on metal deck at the second and third levels is
identical to the north building. On the other hand, the south building has a more typical grid
layout with girders spanning 25’, 30’, or 35’ between columns. The girders and columns come
in various sizes since they were designed cost effectively depending on each member’s
specific loads. The wide flange columns range in size from W8x24 to W14x132, with additional
ten-inch diameter, A53 Grade B structural pipes located in the lobby for aesthetic reasons.
The girders and columns are welded together with simple moment connections in the north-
south direction to provide lateral support and carry floor loads. The second and third floor
beams, all W21x44s, span either 42’-6” (in the west wing) or 40’ (east wing); barring exceptions
where they are split by floor access openings, mechanical shafts, or lateral bracing.
The roof structure is also slightly different
(typical plan, left), using an array of
bbeeaammss1, ggiirrddeerrss, and ooppeenn wweebb sstteeeell jjooiissttss
to carry the cellular concrete plates on
metal decking. Typical roof supports are
30K9s and 28K8s in the east/west
direction, spanning the 42’-6” or 40’,
respectively, between girders. Although,
anywhere there is a ccoolluummnn, the beams
and girders connecting to it are wide
flanges. Beams are connected to the
weak axis with simple shear connections
since they only carry a small tributary area of floor weight. Moment connections, blue
triangles at the end of a girder, are used for the girders running north/south, just as for the
second and third levels. There are a few exceptions in the typical roof grid, such as the atrium
ceiling and extra structural strength at locations of mechanical equipment2.
1 Colors represent members in typical plan, this page 2 See Structural Plans in Appendix B
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 14
LATERAL SYSTEM Design Loads:
• Wind Loads
V 90.0 Basic Design Wind Velocity (ASCE7-98) Iw 1.15 Importance Factor II Occupancy Classification C Exposure Category
GCpi +/-0.18 Internal Pressure Coefficients
Main Wind Force Resisting System:
Vy North Building South Buildng Roof 4.11 7.08 3rd Floor 12.53 21.72 2nd Floor 13.70 23.98 Foundation 7.64 13.22 Total Base Shear 38 kips 66 kips Overturning Moment 809.77 ft-k 1405.61 ft-k
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 15
Vx North Building South Buildng Roof 16.10 36.05 3rd Floor 31.46 70.44 2nd Floor 29.90 66.95 Foundation 14.54 32.57 Total Base Shear 92 kips 206 kips Overturning Moment 2218.72 ft-k 4967.91 ft-k
Components and Cladding: As required by the North Carolina State Building Code, all building
components and cladding engineered by the component manufacturer are to be designed
by the manufacturer’s engineer to comply with the basic design wind velocity, importance
factor, and exposure listed on the previous page.
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 16
• Seismic Loads Seismic Force Resisting System: South Building:
E/W Direction – Steel Concentrically Braced Frames R = 3 N/S Direction – Steel Moment Frames R = 3
North Building: E/W Direction – Steel Braced Frames & Concrete Shear Walls Rmin = 3 N/S Direction – Steel Concentrically Braced Frames R = 3
Design Base Shear: Per Section 1617.4 of IBC Analysis Procedure: Equivalent Lateral Force Procedure
Importance Factor 1.25
Use Group II Design Category B
Site Class C SS 24.9% S1 11.1% Fa 0.0120 Fv 0.0169 Sms 0.0030 Sm1 0.0019 Sds 0.0020 Sd1 0.0013
Direction North Building South Buildng N-S Ry 3.0 3.0 Cdy 3.0 3.0 Vy 95 kips 375 kips E-W Rx 3.0 3.0 Cdx 3.0 3.0 Vx 95 kips 375 kips
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 17
Typical North Building Structural Plan (continued next page)
The north building’s lateral system can be summed up in one word: truss. This design
distributes lateral forces into axial loads along truss chord and web members.
There are trusses spanning the length of the cantilever horizontally at the floor levels.
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 18
Typical North Building Structural Plan
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 19
There are trusses running vertically.
Truss Elevations – Grid Line B
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 20
Truss Elevations – Grid Line C
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 21
The lateral system is broken down into two separate systems, the north/south direction
and the east/west direction.
The north/south lateral system must be extremely rigid since the cantilever’s overhang
spans in that direction. Strong enough winds could cause the cantilever to deflect and tilt
downwards. The stiffness of the trusses in this system also contributes to the amount of
vibration the cantilever will see during an earthquake. Two different types of trusses, one
vertical and one horizontal, make up the bracing in the north/south direction. The vertical
bracing, shown on the previous four pages, is located at grid lines B and C. These trusses
closely resemble a cantilever bridge truss. The two pieces, as they are labeled, are to be
brought to the site preassembled into three different sections each. The sections are split at
each of the splice locations, and once on site, they will be bolted together into the
magnificent trusses as shown. The trusses consist of top and bottom chords that are either
W14x211s or W14x90s, depending on which floor level. The web members are either W14x43s
or W14x90s.
There are also braces at grid line D, to provide stability at the ground floor1. The reason
for this bracing can be explained by comparing the trusses at grid line B and C. Grid line B has
an extra column, at grid line 4.4, and a cross-brace, at the ground floor level between grid
lines 4.4 and 4, that is not found in grid line C’s elevation. The architectural plans2 show that
located between grid lines B and D on the ground floor is a large lecture hall that can not
afford to have a column or cross bracing interrupting the space. Because of this, the brace
must be relocated to grid line D. These two chevron braces are HSS 6”x6”x½” steel tubes.
The horizontal bracing utilizes HSS rectangular tubes bolted in place below the metal
decking at each floor level. Most of the braces are 13’-5” long, Grade 46, HSS 8”x8”x¼” tubes
that are bolted on site. The large cantilever-girders are paired with W14x34 beams to make up
truss chords around the rectangular tubing. The principal depth of the trusses is nine feet,
essentially spanning the entire 106’ length of the north building.
The east-west direction is a mixture of two, 12” thick, reinforced concrete shear walls
and vertical tube bracing3 at grid line 4.9. It also utilizes the floor truss web members as
additional bracing. The two shear walls, located at grid lines 3 and 4, are 46’-5” high, 22’ long
1 Bracing elevation VF#7 found in Appendix D 2 Architectural Plans found in Appendix A 3 Bracing elevation VF#6 found in Appendix D
Mick Leso – Structural Option 2006 Penn State AE Senior Thesis
EXISTING CONDITIONS 22
with reinforcement at each face composing of #5 vertical bars @18” O.C. and #5 horizontal
bars @ 12” O.C. The tube braces are HSS 6”x6”x½” steel tubes.
The south building has a similar lateral bracing system. In the east/west, there are five
additional chevron bracing locations1. Grid lines 5, 7, 9, 11, and 13 all have inverted-V braces
at each floor level over a 27’-
1” span between grid lines B.5
and C. The ground floor
braces are 21’-9” long,
second floor 19’-7”, and third
floor 18’-5”. Each floor has
two HSS 6”x6”x½” rectangular
tubes, one to brace in each
direction. The tube brace
connections in the Renick
Building entail bolting gusset
plates to the web of either the
columns or girders. Then, on
site, the rectangular tubing is
field welded to the gusset
plates with 1-inch wide fillet
welds on both sides.
In the north/south direction,
there are simple moment connections
located at the splice between the
main floor girders and columns. The
welds, as shown here, are to be field-
welded, bevel plug or slot welds. The
beam web is also bolted to the
column flanges.
1 See Bracing Elevations in Appendix D