South Campus Pedestrian
Bridge Proposal
Robert M. Wick
4/22/2011
Construction Engineering Technology
This paper will propose the construction of a pedestrian bridge at the intersection of Exchange
St. and Grant St. just South of campus. The scope of this project includes the following: 1)
Proposal of the location of the bridge, including rationale for such a location; 2) Simple design
analyses, for use in determining material type, quantity, and other pertinent characteristics (for
use in the estimation of cost); 3) Estimation of the cost of such a structure; 4) Development of
simple plans, to aid in building the model and estimating the cost; and 5) Performance of a traffic
survey to gather raw data on foot and vehicular traffic flow. The project does not address funding
sources, legal requirements, in-depth design analyses, or scheduling of the work. This project
applies some of the core aspects of the Construction Engineering Technology program towards a
solution to a real life problem. Ultimately, a rough “ballpark” figure will be determined for
construction of the bridge. Along the way, some of the challenges associated with the proposed
bridge will be discussed. The public benefit of the bridge is twofold: increased safety for
pedestrians and improved traffic flow conditions for vehicles.
Table of Contents
LIST OF TABLES & FIGURES ................................................................................................................ 1
INTRODUCTION .................................................................................................................................. 2
BRIDGE DESCRIPTION & CONSIDERATIONS .................................................................................. 2
BACKGROUND INVESTIGATION....................................................................................................... 4
Survey of Traffic Flow............................................................................................................................ 8
Basic Design Work ................................................................................................................................ 9
The Estimate..........................................................................................................................................11
CLOSING .............................................................................................................................................. 13
REFERENCES........................................................................................................................................ 13
LIST OF TABLES & FIGURES
Figure 1: Close-Up of Suspended Walkway .......................................................................................... 3
Figure 2: front view of exchange apartments ....................................................................................... 3
Figure 3: Bridge Investigation Summary .............................................................................................. 5
Figure 4: Web soil survey of site soil conditions [5] ............................................................................ 6
Figure 5: North deck Bridge Span ......................................................................................................... 7
Figure 6: JAR Bridge Column ................................................................................................................ 7
Figure 7: CBA Support Structure Detail ............................................................................................... 7
Figure 8: North Deck Bridge Hallway................................................................................................... 7
Figure 9: JAR Bridge Span W/ Column Support .................................................................................. 7
Figure 10: Turning Direction Comparison............................................................................................ 8
Figure 11: Strut Detail ........................................................................................................................... 10
Figure 12: Road Classifications of Major Akron Roads [4] .................................................................. 12
1
| Robert M. Wick
INTRODUCTION
With a large majority of students at the University of Akron commuting to class every day,
campus parking is a nightmare. In recent years, the University has attempted to alleviate some of
the parking problems with the construction of new parking decks and the acquisition of new
space for parking lots. Maximizing valuable and limited campus property by fitting more cars per
square inch has created an interesting new problem: outgoing traffic. With so many vehicles
entering and exiting campus on a daily basis, traffic is just an unavoidable fact of life. However,
traffic problems at the southern tip of campus seem to be caused not by sheer volume of cars
alone, but by pedestrians impeding traffic at every light change. The bottleneck occurs when the
light stopping Sumner St. and the parking deck turns green, letting those cars onto E. Exchange
St. As soon as the light turns, groups of pedestrians cross the street from both sides, blocking
vehicle traffic completely. By the time the road is clear, vehicle traffic has only seconds to move
before the light turns red. This process repeats over and over, and is especially evident at peak
times of the day when many people are trying to enter and exit campus, both on foot and in
vehicles. Traffic is regularly backed up from Exchange St. to the old parking deck adjacent to
Schrank South. The least expensive solution to this problem would simply be to lengthen the
amount of time the light stays green. However, this might cause the delays to shift to Exchange
St, which is more critical then traffic on side streets. The proposed solution, and topic of this
paper, is the construction of a pedestrian bridge across Exchange St.
The scope of this project includes the following: 1) Proposal of the location of the bridge,
including rationale for such a location; 2) Simple design analyses, for use in determining material
type, quantity, and other pertinent characteristics (for use in the estimation of cost); 3)
Estimation of the cost of such a structure; 4) Development of simple plans, to aid in building the
model and estimating the cost; and 5) Performance of a traffic survey to gather raw data on foot
and vehicular traffic flow. The project does not address funding sources, legal requirements, indepth design analyses, or scheduling of the work.
This project applies some of the core aspects of the Construction Engineering Technology
program towards a solution to a real life problem. Ultimately, a rough “ballpark” figure will be
determined for construction of the bridge. Along the way, some of the challenges associated with
the proposed bridge will be discussed. The public benefit of the bridge is twofold: increased safety
for pedestrians and improved traffic flow conditions for vehicles.
BRIDGE DESCRIPTION & CONSIDERATIONS
The proposed bridge would be in the vicinity of the Grant St. / E. Exchange Street
intersection, spanning from the Level 2 bay of the South Campus Parking Deck (located between
2
| Robert M. Wick
the existing staircase and elevator room) to the grassy median directly between the Grant St.
Northbound and Southbound lanes, and additionally T-ing off from that location to the Exchange
Street Apartment Complex and to the business area adjacent to Grant St. Northbound (for future
expansion). It would include stairs for street access on the Southern side of Exchange St., since
the parking deck already has a built-in staircase. In this way, it serves the function of allowing
street level pedestrians to safely cross the road, without having to jaywalk or wait for a cross
signal. The bridge would be physically attached to the apartment complex at the lowest-level
suspended walkway (see Figures 1 and 2), which is about 11’ 4” off the ground; however, the bridge
would come in at a height of 15’ 6”, so some additional construction would have to be performed
on the building in order to accept the bridge at this height, which is outside the scope of this
paper.
Taking a walkthrough of the existing parking decks on Level 3 will reveal an existing
pathway through the parking decks; this pathway starts on Level 3 of the new South Campus
Parking Deck, connects to the old parking deck (adjacent to Shrank South) via a small pedestrian
bridge, and ultimately leads to a wider bridge that spans from the old parking deck to the patio
area of Shrank South In order to facilitate logical flow, initial consideration was given to have the
proposed pedestrian bridge connect to the new deck at Level 3; however, the bridge height at this
level would have been over 30’. Not only would the bridge be subjected to greater wind loads at
this height, but the probability of street-level pedestrians using the bridge would likely drop off,
as the height would require a 4-story mountain climb to get up to deck level (using stairs).
Instead, the decision was made to install the bridge at Level 2 of the parking deck. This also has
the added benefit of lowering overall cost, as construction is less hazardous and material
quantities for concrete columns are lessened (as well as the thickness and amount of steel needed
for reinforcement and for structural load purposes). A sign could be placed in the Level 2 bay
directing pedestrian traffic to Level 3.
FIGURE 1: CLOSE -U P OF
SUSPENDED WALKWAY
FIGURE 2: FRONT VIEW OF EXCHANGE APARTMENTS
3
| Robert M. Wick
Direct access to the dorm will be a convenient way for students to quickly get back to
their rooms, and would introduce unique security issues. The bridge exit doors here would
probably require a card swipe, just like any other standard dorm access point. Additionally, the
dorm could be remodeled in that area in order to provide a security/check-in desk, and could be
partitioned in such a way as to make passing the desk the only option. Additional security doors
could be installed just past this point in order to maximize control of personnel traffic (similar to
the system in place inside of Bulger or Spantan Hall). While the construction of these options was
beyond the scope of this paper, they are relevant considerations, and illustrate some of the
thought processes that went into the ultimate placement and implementation of the bridge.
Roadway clearance height was also an important factor to consider. Exchange St. is
classified by ODOT as a “Minor Arterial” road [4] (See Figure 13). The City of Akron also has an
ordinance stating, “All bridges hereafter designed over city streets and highways, including both
controlled and uncontrolled access facilities, that are considered nonstrategic by the federal
government, shall have a minimum clearance over the highest point of the road surface, including
berms, under the bridge, of fifteen feet, four inches” [2]. Therefore, the bridge was designed to not
be less than 15’ 6” in height at any point, except at dorm connection points.
BACKGROUND INVESTIGATION
Site investigation is a crucial step in any construction or design process. Conveying
valuable clues and insights about the condition and context of the site, it’s an initial step that is
sometimes neglected, often causing unforeseen complications later on. The site investigation for
the proposed bridge consisted of several activities, including measurement of critical site
dimensions, noting of general site conditions, site photography, office reconnaissance, existing
bridge investigations, and site sketching.
A general reconnaissance of the area was performed prior to starting any other activity in
order to gain familiarity with the area. The first problem to solve was the placement of the bridge
itself. Several questions came to mind when trying to decide where and how to place the bridge.
Where are the majority of pedestrians traveling from (Sumner St. or the Exchange Apartments)?
Where will the bridge be most conveniently placed? How can it be placed so as not to impede
vehicular traffic (due to the increased pedestrian traffic)? It was ultimately decided to place the
bridge at the location described above due to the possibility of future UA dorm construction in
the business area, which would greatly increase the number of students traveling from that area
and crossing the street (not to mention it takes advantage of the 3rd level parking deck walkways).
Other items noticed on the reconnaissance included the possibility of moving the street light near
the parking deck, adding protection for an existing utility box on the grassy median, removal of a
street light on the grassy median, and several trees that would likely have to be removed
throughout the area.
4
| Robert M. Wick
Measurement of the various site dimensions was taken using a standard 16’ metal tape
measure. All measurements were taken with a reasonable degree of care to ensure approximate
values were obtained; however, these measurements, ultimately forming the baseline for the cost
estimate, were not meant to be exact. A summary of the measurements taken can be seen
throughout the simple drawn plans. Major areas requiring actual dimension numbers for project
planning purposes include the parking deck, E. Exchange St., the grassy median, Grant St., and
the sidewalk area of the Exchange Street Apartment Complex (the dimensions obtained from
these areas were mirrored for the business area, with the assumption that any future buildings
there would be built to connect to the bridge).
Office reconnaissance can be a useful tool when trying to discover information about the
site. Especially in urban areas with ongoing construction projects, a multitude of information may
be available without having to leave the office. One instance of office recon from this project was
the use of the USDA’s Web Soil Survey Program [5], which stores soil data from all over the
Existing Bridge Investigation Summary
Bridge Inspection Results
Span
Width
Interior Height
Support Pillar
Circumference
North Deck
87' 4"
7' 2"
10'
NA
JAR - Long Section
JAR - Short Section
~85'
~76'
NA
NA
NA
NA
9.5'
9.5'
CBA-Polski
126' 8"
10' 7"
9'
NA
Stairway Inspection Results
Length of Stair Set
Height /
Parking
Deck
Level
13' 8"
13' 9"
10' 9"
14' 2"
9' 4"
10' 7"
Ave. Height / Stair Height / Stair Set Width of Stair Set
North Deck
7"
Polski
7"
5' 4"
FIGURE 3: B RIDGE INVESTIGATION SUMMARY
5
| Robert M. Wick
United States. By selecting an area of interest, one can learn about various characteristics and
aspects of underlying soils for a given area. Selecting the area spanning from Buckeye St to
Sumner St (see figure 3), the survey returned a variety of data on the area. For instance, from the
ground surface to 79” in depth, the soil is composed primarily of silt loam and loam [5], which are
not ideal soils to build upon. The water table depth (12-24”) is also given [5], as is the corrosion of
concrete rating (an important consideration to make for design of concrete foundations). The
survey advises that the site’s suitability for small commercial buildings is “somewhat limited” [5]
FIGURE 4: WEB SOIL SURVEY OF SITE SOIL CONDITIONS [5]
To complete the research into the proposed bridge, research of existing bridges
was conducted. Specifically, the bridges studied included the North Campus Parking
Deck Bridge, the now defunct pedestrian bridge at the JAR, and the bridge connecting the
CBA to the Polski Building Parking Deck (located on the top floor of the deck).
Measurements taken about each structure are summarized in Figure 4. Various designs
were used on each bridge, and the proposed bridge borrows and/or mixes ideas from
each. For instance, the JAR bridge has a similar span to the proposed bridge, so its pillar
foundations were chosen to be the model for the estimate. Likewise, the width of the
proposed bridge was chosen to be between the North Deck Bridge and the CBA bridge
due to each seeming too narrow and too wide, respectively. Pictures were also taken of
each bridge, highlighting general setting, structural members, and construction
techniques, among other features (see Figures 5-9). Stairways in the North Deck and
Polski Deck were also analyzed in a similar fashion.
6
| Robert M. Wick
FIGURE 5: NORTH DECK BRIDGE
SPAN
FIGURE 6: JAR BRIDGE COLUMN
FIGURE 8: NORTH DECK
BRIDGE HALLWAY
FIGURE 7: CBA SUPPORT
STRUCTURE DETAIL
FIGURE 9: JAR B RIDGE SPAN W/ COLUMN
SUPPORT
7 | Robert M. Wick
Survey of Traffic Flow
A survey was taken to assess the general traffic conditions of the Sumner St. / Exchange St.
intersection. The survey was taken at various times for 2 days, and care was taken to perform the
survey at peak times (times between when classes generally finished and started, campus-wide)
and at off times (mid-afternoon or non-common class times). The survey included data on a
number of factors, including the number of cars waiting on either side of the intersection, which
direction they turned, how many were “left behind” after the light turned red, the average light
cycle of both the N/S and E/W facing lights, the number of people on either side of the street, the
average pedestrian crossing time, the time and day, and the weather.
The survey was performed using a stopwatch and a premade spreadsheet for recording of
data. The top floor of the new South Campus Deck was used as the vantage point, as it gave a
good view of the entire area, except for the area between the deck and Shrank South, which
hindered results slightly when traffic backed up beyond that area. A complete summary of the
survey results can be seen in the attached spreadsheet under the “Survey Raw Data” tab; Figure 10
Turning Direction Comparison
5
33
Sumner St: Right
Sumner St: Left
25
Deck: Right
76
0
10
20
30
40
50
60
70
Deck: Left
80
Number of Cars
FIGURE 10: TURNING DIRECTION COMPARISON
illustrates an interesting find of the survey, however. It can be seen that the number of cars
turning left out of either street easily dwarfs the number of right-hand-turning vehicles. Based on
this data, traffic flow through the area could probably be at the very least somewhat improved if
left-hand turning lanes were installed on either or both streets, especially near the parking deck.
This would allow cars turning right or going straight to pass, relieving at least some of the traffic
build-up.
8
| Robert M. Wick
In general, the traffic conditions at the intersection seem manageable. However, at peak
times, on-campus traffic can back up quite extensively. The average light cycle for the N/S facing
lights (affecting people trying to leave campus) was 30 seconds (in contrast, the average light
cycle for Exchange St. was 62 seconds). The average time taken for pedestrians to clear the street
was 10 seconds; the longest witnessed was about 15 seconds, while the shortest was about 7
seconds. With medium-low traffic conditions (Tuesday results), the average line of cars on
campus was 6, with the average being kept behind was 1. At times with peak traffic (Thursday
results), the average backup was calculated to be 5; however, error is probably the culprit of this
result, as the first four iterations of that survey resulted in backups of more than 9 cars (the line
wrapped around the deck and out of view, but was presumably more backlogged than that). The
error may have come from the fact that true value of peak time backups was limited by the sight
issue, and should have been greater. The final iteration had a car backup of just 1, which was
thrown out as an outlier for the calculation of average.
While the survey did reveal some valuable information, some of the results came out
slightly skewed, due to several reasons: 1) Taking note and tracking all of the different bits of
information within an average 30 second time frame became increasingly difficult as the number
of cars backed up increased; 2) Weather may have an effect on the results of any particular survey
(more people would likely walk instead of drive to campus on a warm sunny day, and vice versa, if
they have the option); 3) Prior to the survey being performed, the light signal was altered in an
indeterminate way. Crossing lights were updated to display the amount of time left before the
light turned red, which was a noticeable change. It’s possible that the light cycle was also changed
to help improve traffic flow in the area, though this is simply speculation.
Basic Design Work
Although this project was not a design project, some simple design calculations were used
to provide a more realistic structure, which is also reflected in the plans. Simple beam design was
used in order to select the structural steel members of the bridge, and also played a role in
choosing the support structure of the bridge. The following analyses will walk through the
calculation of the bridge girders crossing over Exchange St. only, though the same process was
applied to all beams.
Beam selection criteria analyses begins with the calculation of beam moment, given by the
following equation:
where M is the moment, w is the load, and l is the length of span. Using general industry
“average” values for the dead and live loads (100 # / ft^2 each), and multiplying that by 5’ (one half
9
| Robert M. Wick
of the proposed bridge width, the width that each of the two girders is responsible for), and
covering a span of approximately 103’ (from Parking Deck to grassy median), the equation
becomes:
Using this value for M, the value of the minimum Section Modulus Sxx required can be found
using the following:
where Sball is the allowable bending stress. An S ball value of 24000 psi was selected (as done in a
typical conservative calculation). Plugging this into the equation, and multiplying M by 12” / 1’
(convert from feet to inches) yields an S xx value of 663 in3. This is the minimum value that S zz can
be for a beam to function safely in its application, so several beams with higher values of Sxx were
considered (summarized in the “Girders” section of the attached spreadsheet under the “Steel “
tab). This value of the Section Modulus forces the selection of very thick beams; it was decided to
add steel support struts to the bridge that would intersect it 16’ (linearly) from the parking deck
and grassy median pillar, respectively (see figure 11).
FIGURE 11: STRUT DETAIL
10
| Robert M. Wick
Because of the unfavorable in-situ soils within the project area, deep foundations were
selected as the method of transferring the load of the bridge to the ground. Two main methods of
installing deep foundations were considered: driven piles and augered piles. However, given the
urban setting of this application, and the existence of nearby structures, driven piles were
discarded as an acceptable method of installation, due to noise and vibration issues. Instead,
Augered-Cast-In-Place (ACIP) piles were selected as the method of installation, since noise and
vibration are reduced as compared to driven piles. Three columns would support the bridge; one
at the sidewalk area of the Exchange Dorms (Column 1), one at the grassy median (Column 2),
and one at the business area sidewalk (Column 3). These columns would each be 3’ 2” in diameter,
and 15’6” in height from the ground to the bridge, and would also extend an additional 15’ from
the ground surface into the earth (assumed to be bedrock at this depth for estimate purposes).
Additionally, two more columns would be installed to support the staircase structure for street
level access, with diameters of 2’ and a total height (from ground to bedrock) of 15’. The selected
column diameters were based upon the design of the JAR columns, which measure the same,
since the JAR bridge has a similar span length and span design.
The Estimate
The estimate was based primarily off of the measured field dimensions of the site, the
simple plan drawings, and the basic design assumptions and decisions mentioned previously.
Quantity takeoffs were performed using the attached spreadsheets (all sheets from “Structure
Specs” through “Lights”). Utilizing the estimation program Win Estimator, a final cost was
computed for the project. This cost includes estimations of labor, material, and equipment costs,
based on industry-wide cost averages. Major work categories include steel, concrete (which also
includes formwork, rebar, curing, and finishing), doors and windows, excavation, and electrical
(light fixtures). The net cost of the project was calculated to be $196,561.38. Also taking into
consideration a 12% overhead and profit tack-on (not applied towards labor) gave a total project
cost of $215,806.37. By far, the largest cost area for the project was material cost, comprising
80.84% of total project cost (before O&P). This may not be too unreasonable, as the bridge
contains a large quantity of steel, which has a high material cost association.
11
| Robert M. Wick
FIGURE 12: ROAD CLASSIFICATIONS OF MAJOR A KRON R OADS [4]
12 | Robert M. Wick
CLOSING
The South Campus Pedestrian Bridge Project gives a rough estimate of the cost to build a
pedestrian bridge at the Exchange St. / Grant St. intersection. Many items were left off the table
(such as insurance bonds, permit fees, taxes, scheduling, and bidding) that would be present in a
real-life construction scenario; however, the purpose of the project was to provide some rough
idea of the cost to build such a structure. The survey was another tool used in the project to
illustrate the traffic problem in detail. The on-site investigation was another keystone of the
project, and was a prerequisite that had to be finished before any of the other project sections
could start, since it gave reference points to start from. It is difficult to correlate safety or
convenience to actual dollar amounts, but given the size and traffic flow of Exchange St., this may
be one construction project worth investing in.
REFERENCES
1. Chapter 3: The 13 Controlling Criteria - Vertical Clearance. U.S. Department of
Transportation: Federal Highway Administration, n.d. Web. 2011.
<http://safety.fhwa.dot.gov/geometric/pubs/mitigationstrategies/chapter3/3_verti
calclearance.htm>.
2. Akron, Ohio, Code of Ordinances (Title 9, Chapter 98, Article 2. - Streets). City of
Akron, n.d. Web. 2011.
<http://library.municode.com/HTML/16028/level3/TIT9GEPR_CH98STSI_ART2S
T.html#TIT9GEPR_CH98STSI_ART2ST_98.15BR>.
3. "Regulations for Construction and Special Activities in Streets Rights-of-Way."
Akron, Ohio, Code of Ordinances (Title 9, Chapter 98, Section 98.42). City of Akron,
Department of Public Service, Bureau of Public Works. 2 Feb. 2009. Web. 2011.
<ci.akron.oh.us/PubWrks/forms/ROWRegs.pdf>.
13
| Robert M. Wick
4. "Akron North Central." Functional Classification Maps. Ohio Department of
Transportation, n.d. Web. 2011.
<http://www.dot.state.oh.us/divisions/transsysdev/programmgt/functionalclass/pages/fu
nctionalclassificationmaps.aspx?View={9138960C-9980-4B7C-9E2A-BF10AA10EAD8}>.
5. Web Soil Survey. USDA Natural Resource Conservation Service, n.d. Web. 2011.
<http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx>.
14
| Robert M. Wick