PSPE News

Abstract (Click here to see abstract with grids.)
Matthew A. Balmer, P.E.

In the field of power electronics, there is an ongoing search for an ideal solid-state power switch which has a low on-state resistance, low switching losses, high operation frequency, and good thermal capabilities. Silicon-Carbide (SiC) technology is a proven forerunner in the quest for the ideal solid-state power switch.

SiC technology represents a disruptive technological innovation for the 21^st century that will establish new trajectories for electronic innovations obsoleting the silicon technology of the 20^th century.  SiC technology has found a niche in small device applications and is a nascent technology being commercialized into power electronics.  Testing of SiC power electronics has demonstrated improved efficiencies, reduced size and reduced weight when compared to conventional Si based technology.

This paper explores

• SiC Technology Introduction,
• SiC Technology Power Electronics Advantages, and
• SiC Technology Commercialization.

Sic technology introduction

The challenge in the semiconductor industry is to maximize efficiency, reduce size, increase power quality and reduce costs.  Researchers have learned that using Wide Bandgap (WBG) materials, such as Silicon Carbide (SiC), allows semiconductor components to be smaller, faster, more reliable and more efficient than the existing Silicon (Si) technology [1].

 Characteristics SiC Technology

Silicon carbide morphology is a binary combination of two group IV binary elements having an equal number of silicon and carbon atoms arranged in a hexagonal lattice structure. This atomic structure makes SiC one of the hardest and most thermally stable materials known [1].  Additional, features such as increased avalanche breakdown voltage, high thermal conductivity, and decreased thermal leakage current have created great interest in SiC technology for use in high power applications.  Microscopic studies of the stability and rupture of molecular junctions under a high voltage bias discovered that semiconductors having a SiC backbone have higher probabilities of sustaining higher voltages [2].

 Wide Bandgap (WBG) Technology

Bandgaps determines how a material’s electrons behave. Electrons are negatively charged particles that surround a nucleus at different energy levels.  When electrons move together in the same direction they form an electric current.  Electrons in an atom exist in various states which includes their energy level, momentum and spin.  Furthermore, quantum mechanics states two electrons cannot exist in the same state at the same time; therefore, one variable must differ.

These sets of possible states form regions called bands. Sets of states that are not possible form regions between the bands called bandgaps.  Bands closest to the nucleus of an atom are called core level and the band containing electrons furthest from the nucleus are called the valence band.  Beyond the valence band is the conduction band where the electrons can move freely, figure 1.

Examining various materials (Figure 2), metals have an overlapping valence and conductions bands and electrical current easily flows through them. On the opposite end are insulators, which have a wide gap between the valence band and conduction band reducing the probability to move an electron from the valence band to the conduction band.  The third and most interesting materials are semiconductors which can have properties like a metal, an insulator, or properties in between.

When semiconductors were first discovered, they were considered useless because of their erratic unpredictable behavior. Once bandgap properties were understood, physicists and engineers were able to harness bandgaps to innovate new technologies.  It was also discovered that valence electrons became exited by heat, light, or an electric field and will jump the bandgap (figure 1) provided the bandgap’s width allows the electrons to jump to the conduction band.  Consequently, different electronic devices require materials with different bandgaps which is relative to the energy supplied by the energy source.  Table 1 lists common semiconductor materials with their bandgap energy levels and application.

SiC: Power Electronics Advantages

Power Semiconductor Construction

Power semiconductors are unique when compared to that of low power signal semiconductors. Low power semiconductor devices are required to carry a few amperes under forward biased conditions and block small voltages under reverse biased conditions.  However, power semiconductor devices are required to carry hundreds of amperes in forward biased condition and block several hundred to thousand volts in the reverse biased condition.  These extreme operating conditions require a structural change affecting the operating characteristics.  These operating conditions create an inherent contradictory condition for power semiconductors, in that, increased doping reduces the forward losses and also reduces the reverse breakdown voltage, with the converse being true.  This contradiction is eliminated by the addition of a lightly doped epitaxial layer (drift region) whose doping density is 10¹⁴cm^-3 between the heavily doped p and n regions whose doping density is 10¹⁹cm^-3.

Figure 3 depicts the construction differences between low power and high power semiconductor devices.

This epitaxial layer creates a uniform electric field between the p and n junction that reduces the forward voltage drop and increases reverse blocking voltage.

Reduced Power Loss

Reduced power losses create increased savings for the consumer. SiC wide bandgap has a critical field for avalanche breakdown that is 10 times greater than Si.  This reduces the width of the epitaxial layer by one-tenth that of Si.  The result is SiC has a specific forward conduction resistance 400 times lower than Si thus reducing power losses [2].

 High Temperature Operation

SiC intrinsic characteristics allow SiC based semiconductors to operate at higher junction temperatures. The intrinsic characteristics include:

• SiC based semiconductors have a melting point of approximately 2,700^oC, whereas Si based semiconductors have a melting point of approximately 1,400^oC.
• Thermal leakage current is proportional to a compound’s intrinsic carrier concentration.  SiC has an intrinsic carrier concentration that is in order of magnitudes less (10^-18) than Si [2].
• SiC has a bandgap three times that of Si prohibiting excessive thermal leakage current.

The combination of these intrinsic features allows SiC devices to operate at junction temperatures reaching 600^oC compared to Si which has a junction temperature limit of 150^oC.

 High-speed Switching Operation

SiC wide bandgap has a high dielectric breakdown voltage which reduces power losses during switching operation. Figure 4 depicts the forward recovery time for an SiC Schottky Barrier Diode.  The Si overshoot represents an accumulation of charge carriers in the epitaxial layer that must diffuse prior to re-switching.  In addition, the Si overshoot is also indicative of heat generation in the device created by the simultaneous current and voltage overshoot.  SiC has an epitaxial region one-tenth the size of Si which results in a reduction of overshoot, a faster forward recovery time and reduced power loss.

Heat Dissipation

SiC intrinsic thermal conductivity, the ability to remove heat, is twice that of Si [1]. SiC has a thermal conductivity of 3.3W/cm^oK contrasted to Si which has a thermal conductivity of 1.5W/cm^oK. SiC’s increased heat dissipation means SiC devices can operate with a reduced temperature drop across the device making it ideal for power applications.

SIC COMMERCIALIZATION

 SiC: A Disruptive Technology

The Institute of Electrical Engineers (IEEE) states silicon carbide may be to the 21^st century what silicon was to the 20^th century [3].  Furthermore, the US Department of Energy considers WBG semiconductors to be a foundational technology that will transform multiple markets and industries, resulting in billions of dollars of savings for businesses and consumers when use becomes widespread [4].  WBG semiconductors permit devices to operate at much higher temperatures, voltages, and frequencies making the power electronic modules using these materials significantly more power and energy efficient than those made from conventional semiconductor materials [4].

SiC technology is a disruptive technology that has change the trajectory of future semiconductor innovations. Topologies of technological change are divided into two distinct categories:  Sustained or Disruptive [5].

A sustained technological change maintains the industry’s rate of product performance trajectory; these are process innovation and less product innovation. An example of sustained technology change was in the early use of computer memory disk drive industry.  Computer memory disk drives were introduced circa 1976 and with a recording density of 1 million bits/square inch.  These disk drives used particulate oxide disk technology and ferrite head technology (oxide/ferrite) [5].  From 1976 to 1985, oxide/ferrite recording density grew linearly to 10 million bits/square inch.  The recording density growth was related to incremental advances in manufacturing techniques such as grinding the ferrite heads, more precise dimensions, and using smaller more finely dispersed oxide particles on the disk’s surface [5].

In 1985, the oxide/ferrite storage technology reached its maturity and the recording density began to level-off. The maturity of the oxide/ferrite technology created a search for a new technology which introduced an incremental advance to thin film and head technology starting a new trajectory.

A disruptive technological change is governed by an innovation discontinuity which redefines the performance trajectory leading to creative destruction overturning the established industry structures [5].  Furthermore, discontinuous innovations are competency destroying, obsoleting existing know-how because mastery of the old technology does not imply mastery of the new [5].  In the 20^th century, the disruptive technology was the introduction of silicon based electronics which replaced vacuum tubes and sparked the evolution electronics that revolutionized the world.

In the 21^st century, the integration of WBG technology will set a new course for all industries.  The Department of Energy (DOE) has indicated WBG semiconductors will pave the way for exciting innovations in power electronics, solid-state lighting and other diverse applications across multiple industrial and clean energy sectors [4].

Commercially Available SiC Power Devices

Mitsubishi Electric has commercialized SiC technology into fundamental power semiconductor devices that include Schottky Barrier Diodes (SBD) and Metal Oxide Semiconductor Field Effect Transistor (MOSFET). More important, Mitsubishi has commercialized SiC technology into both full and hybrid Insulated Gate Bipolar Transistors (IGBT) and Intelligent Power Modules (IPM).  These full and hybrid SiC IGBT products offer the following advantages over the existing Si technology:

• Reduced switching losses;
• Increased system efficiency;
• High temperature operation;
• Increased operating frequency;
• Reduced cooling requirements;
• Low inductance for increased switching speed; and
• Reduced system size = increased power density.

The full SiC IGBT modules have attained a 70% reduction in inverter power losses and the hybrid SiC IGBT modules have attained a 45% reduction in inverter power losses. Both products have found applications in a plurality of industries which include:

• High power inverters for traction drives, Uninterruptible Power Supplies, and renewable energy applications.
• Small inverters for household appliances and HVAC equipment.
• High frequency inverters for medical equipment and welding.

 SiC Power Application: Mitsubishi Ginza Subway Line Retrofit

SiC technology development has focused on small device technology. However, Mitsubishi Electric introduced SiC technology into power electronics through the development and testing of SiC inverters for Japan’s Ginza subway line [6].  Mitsubishi’s test results are summarized as follows:

• The SiC based inverter was 40% smaller and lighter than the conventional inverter;
• Energy savings was 38.6% compared to the conventional system; and
• Increased regenerated power to 51% compared to 22.7% for the conventional system [6].

These favorable results have prompted Mitsubishi Electric to commercialize the technology and have received 127 orders for the SiC-based inverters [6].

CONCLUSION

SiC technology is a disruptive technology that will establish a new trajectory for small device and power electronics. Tests have demonstrated that SiC based power electronics is smaller, lighter, and more efficient than the existing Si based technology.

REFERENCES

1. Ren, F., Zolper, J.C. Wide Energy Band Electronic Devices.  World      Scientific Publishing, 2003
2. Li, Haixing, Su, Timothy, Zhang, Vivian, etal.  Electric Field    Breakdown in Single Molecule Junctions.  Journal of the American    Chemical Society, 2015, pp 5028 – 5033.
3. IEEE Spectrum, Vol 52, no.5 (INT) May 2015, Front Cover.
4. Wide Bandgap Semiconductors: Pursuing the Promise.  US Department of   Energy, Advanced Manufacturing Office.
5. Tushman, M. L. & Anderson, P. Managing Strategic Innovation and Change.  Second edition, Oxford University Press, 2004.
6. IEEE Spectrum article retrieved from       http://spectrum.ieee.org/semiconductors/devices/silicon-carbide-  ready-to-run-the-rails

Take the 2018 Milton F. Lunch Ethics Contest Challenge!

Download the full contest flyer (PDF)

All current NSPE individual members through their NSPE state societies and NSPE chapters (including student chapters) are invited to participate in the 2018 NSPE Milton F. Lunch Ethics Contest. Match your wits and knowledge of engineering ethics with experienced professional engineers and engineering students throughout the country.

This year the winning entry will receive an award of $2,000 to the author provided by NSPE, a certificate, and recognition in PE magazine.

How to Participate

NSPE’s Board of Ethical Review is furnishing you with two different fact situations to choose from regarding the ethics of engineers or, new this year, you can submit your own case! Please choose any one out of the two situations (or use your own case) and develop an essay, video, photo essay, poster, or PowerPoint presentation which could include embedded videos/sound, etc. to demonstrate your understanding of the facts and the NSPE Code of Ethics. Contestants are asked to read the facts of the case, then develop a discussion and conclusion to respond to the included question(s). Contestants should also provide references, citing specific sections of the NSPE Code of Ethics for Engineers. A copy of the NSPE Code is attached for your reference. Contestants may also want to check the NSPE Board of Ethical Review’s Web site for additional cases decided by the BER.

Contest Rules

All entries must be received by Friday, April 27, 2018. E-mail or mail entries to:

2018 NSPE Milton F. Lunch Ethics Contest
NSPE Legal Department
1420 King Street
Alexandria, VA 22314
E-mail:  legal@nspe.org

The contest is named for NSPE’s former general counsel, who played a key role in the founding of the NSPE Board of Ethical Review.

Every year, we administer the QBS Awards, recognizing public and private entities that make exemplary use of the qualifications-based selection process at the federal, state and local levels. QBS Award winners serve as examples of how well the QBS process works, and they help us promote the practice of QBS in jurisdictions that do not use, or underutilize, QBS to procure engineering services. We are now seeking nominations for the 2018 QBS Awards. The deadline for nominations is Wednesday, February 21, 2018. Nominations must originate from an NSPE State Society, an ACEC Member Organization, a public or private entity, or an individual in the public or private sector. Self-nomination is not permitted. Please mail or email nominations to John Keane with NSPE at jkeane@nspe.org and Charles Kim with ACEC at ckim@acec.org. The QBS Award winner will have an opportunity to receive an engraved trophy and will be recognized during the 2018 NSPE Professional Engineers Conference (PECON) in July 2018 at Caesars Palace in Las Vegas. To learn more, please see the nominations form. QBS Awards Call for Nominations Now Open Until February 21, 2018 | National Society of Professional Engineers —————————— John Keane Policy & Advocacy Associate National Society of Professional Engineers Alexandria VA ——————————

 

ALEXANDRIA, Va. (May 3, 2017) – The National Society of Professional Engineers (NSPE), as the recognized voice and advocate of licensed professional engineers, is aware of and interested in the recent lawsuit filed against the Oregon State Board of Examiners for Engineering and Land Surveying challenging the Oregon Board’s application of the Oregon Professional Engineer Registration Act and Oregon Administrative Rules relating to the use of the title “engineer” and the “practice of engineering.”

NSPE stresses that since this matter is in the initial stages of litigation in federal court, all of the relevant facts and circumstances in the lawsuit are not yet known: much of what is being asserted as fact by the parties, and in social media, is not only incomplete but also in dispute. This includes the facts related to the Oregon Board’s state interest in investigating and prosecuting the matter, allegations of harm by the litigants, and other issues. Accordingly, it is inappropriate for NSPE to comment specifically on this lawsuit until all the facts of the matter are established. NSPE continues to closely monitor ongoing developments, and is fully committed to taking all appropriate steps to ensure that the integrity and the credibility of the engineering licensure process is preserved and protected in furtherance of the public interest.

Since the enactment of the first state professional engineering licensure law in Wyoming in 1907-and more recently in such matters as the Kansas City Hyatt Regency Hotel collapse hearings, the Texas A&M bonfire investigations, the Deepwater Horizon Oil Spill investigations, and the Hurricane Sandy inquiries-state engineering licensure laws have sought to ensure that qualified individuals practice in a manner that safeguards the welfare of the public.

“It is NSPE’s view that engineering licensure serves to hold individuals accountable for the ethical and competent practice of engineering,” said Kodi Verhalen, P.E., Esq., F.NSPE, president of NSPE. “The ultimate role of licensure is the protection of the public health and safety.”

The vital public interest role served by professional licensure of engineers is clear. Licensure ensures that the people who design and maintain the infrastructure and technology around us are not only competent to do so, but also accountable and place the public’s interest above all other considerations. NSPE, as an integrated network of national and state societies working in collaboration, will actively pursue legislative and regulatory action to ensure the continued ability of the state engineering licensure process to fully protect the public.

* * *

The National Society of Professional Engineers is a member-centric, nimble, future-focused, and responsive organization, serving as the recognized voice and advocate of licensed Professional Engineers. Through education, licensure advocacy, leadership training, multidisciplinary networking, and outreach, NSPE enhances the image of its members and their ability to ethically and professionally practice engineering. Founded in 1934, NSPE serves more than 31,000 members and the public through 52 state and territorial societies and over 400 chapters. For more information, please visit www.nspe.org.
——————————
Kodi Jean Verhalen, PE, F.NSPE, Esq.
2016-2017 NSPE President

Harrisburg, PA – After extensive review, the Pennsylvania Department of Environmental Protection (DEP) has approved the permit applications from Sunoco Pipeline LP (Sunoco) for the PA Pipeline Project/Mariner East 2 pipeline project. DEP considered 17 Chp. 105 (Water Obstruction and Encroachment) permits and 3 Chp. 102 (Erosion and Sediment Control) permits for the project. The pipeline would transport natural gas liquids from southwest counties to Marcus Hook, in southeast Pennsylvania.

“I am proud of the immense undertaking our staff took to hold this project accountable within the confines of state law and DEP’s role in this process over the last few years,” said Acting DEP Secretary Patrick McDonnell. “This was a huge undertaking – holding five hearings during a 60-day comment period, reviewing permit applications and technical deficiencies for more than 20,000 hours, responding to 29,000 comments, and ensuring Sunoco addressed deficiencies identified in its initial applications.”

The project required a Chp. 105 permit for each of the 17 counties it crosses, as well as one Chp. 102 permit for each DEP region the project crosses (the Southwest region, the South Central region, and the Southeast region).

“The intensive review included input and feedback from scores of DEP biologists, wetland ecologists, engineers, legal staff, and permit reviewers. Further conditions were put on the operator as we move forward to ensure accountability to state standards,” explained McDonnell.

Part of the review process included revisions to the original permit applications submitted by Sunoco. These revisions were received in December 2016, in response to technical deficiency letters sent by DEP in September 2016. The final approvals include conditions in both the Chp. 102 and Chp 105 permits to establish environmental protections specific to this project.

DEP did not hold an additional public comment period or hold additional hearings because the revisions Sunoco made to the applications did not substantively change right-of-ways nor the corridor of the permits. Previously submitted comments were still applicable.

DEP’s obligation is to ensure that installation of infrastructure like pipelines is in accordance with the relevant regulations, and that concerns raised by commentators were addressed within the scope of those regulations.

“This is not the end of the process, as DEP, working in conjunction with the Public Utility Commission, will continue to hold the project accountable to regulatory standards that protect the environment and ensure the health, public safety, and welfare of local communities,” said McDonnell.

More information on the Mariner East 2 pipeline project can be found here.

MEDIA CONTACT: Neil Shader, 717-787-1323

National Lighting Bureau: Disturbed sleep patterns are common among the residents of senior-care facilities, due to the aging process and diseases like Alzheimer’s. Could lighting make a difference? That’s the question that the Sacramento Municipal Utility District (SMUD); the ACC Care Center, also in Sacramento; and the U.S. Department of Energy (DOE) decided to answer, at least on a preliminary basis, by replacing some of the Care Center’s fluorescent lighting in one corridor, two resident rooms (including bathrooms), the nurse station, the common family room, and the administrator’s office.

Unlike the Care Center’s incumbent fluorescent lighting, the new, replacement lighting provided “tunable white light”; i.e., white-light whose spectral components can be adjusted to create different effects, thanks to the versatility of the light-emitting diodes (LEDs) that serve as the lighting’s illumination source. In this case, the researchers were particularly interested in how the spectral adjustments – tuning – might affect residents’ melatonin levels. (Melatonin is a bodily produced hormone that regulates sleep and wakefulness. It’s also an antioxidant and so has a role in cell repair and as an anti-inflammatory. In humans, melatonin levels in the blood rise and fall during a person’s 24-hour sleep/wake cycle, or circadian rhythm, with high levels at night and low levels during the day.)

Applying guidelines developed by the Lighting Research Center of Rensselaer Polytechnic Institute, researchers used controls to create light whose lumen output and spectral composition were likely to suppress melatonin production from morning to midday, but less likely to suppress melatonin production in the evening and at night.

Results of the study, documented in a new research report, were startling:

• agitated behaviors such as yelling and crying decreased among three residents studied;
• the need for psychotropic and sleep medications was significantly reduced for one of the residents;
• the number of recorded patient falls decreased in the corridor studied; and
• according to ACC staff, residents whose rooms were located elsewhere were now “hanging out” in the LED-illuminated corridor.

According to National Lighting Bureau Chair David R. Errigo (LumenOptix, Inc.), “The study is too small to generate unquestionable conclusions. However, the study’s results seem to validate many emerging hypotheses about both natural and electric lighting’s ability to have vital impacts in health-care facilities, especially those facilities that serve the needs of the elderly. To some extent, the more we learn about lighting, the more we realize what we don’t yet know, with the key word being ‘yet.’ The pace of research is accelerating at a rapid rate; new findings seem to be reported weekly. This is an extremely exciting and extraordinarily optimistic time for those of us involved in lighting, as we seek to understand what lighting can do beyond its traditional role as an aid to human vision.”

The U.S. Department of Energy (DOE) report about this project – Tuning the Light in Senior Care: Evaluating a Trial LED Lighting System at the ACC Care Center in Sacramento, CA – is available free of charge from the National Lighting Bureau.

Obtain more information about the Bureau by visiting its website (www.nlb.org) or by contacting its staff at info@nlb.org or 301/587-9572.

Tyler J. Barile, E.I.T. City of Philadelphia, Streets Department, Bridge Section
Audrey A. Corrado, P.E. Michael Baker International, Philadelphia, PA
Christopher J. Menna, P.E. Jacobs Engineering Group, Former City of Philadelphia, Streets Department, Bridge Section
James B Miller, P.E. Michael Baker International, Philadelphia, PA
Christopher J. Renfro, E.I.T. City of Philadelphia, Streets Department, Bridge Section
Michael J. Schickling, E.I.T. City of Philadelphia, Streets Department, Bridge Section

IBC – 08-75

Abstract: The project involved the reconstruction of a unique, three-span, shallow depth, steel stringer bridge in the Chestnut Hill West Section of Philadelphia. The structure had reached the end of its useful life, having already undergone two emergency repair projects. Innovative reconstruction concepts were advanced to satisfy historic preservation criteria and to restore the structure’s place in the neighborhood.

Background

The original Willow Grove Avenue Bridge over Southeastern Pennsylvania Transportation Authority (SEPTA) tracks was a three-span, simply supported, shallow depth, steel stringer bridge with asphalt deck, as rehabilitated in 1962, with stone masonry abutments and wing walls that dated to 1884. The original double iron channel and timber superstructure was built by the Edge Moor Bridge Works for the Pennsylvania Railroad and designed for a live load of horse and carriage. Built during the industrial revolution, the structure was built to provide grade separation for a street crossing in a very affluent, new neighborhood in Philadelphia – a suburban setting to house railroad and industrialist corporate executives and their families. The original and existing bridges featured materials appropriate for the area – timber, metal, and Wissahickon Schist stone. Though decidedly inelegant, the first and second bridges provided a practical solution to challenging design features– a short hump crest vertical curve nestled between two driveways and incorporated into the site design and functionality of a commuter railroad train station. Originally spanning over two mainline tracks and a siding for an ice house, the current bridge spans over two electrified tracks between the piers. The bridge is contained within the Chestnut Hill Historic District, but is not a contributing element, nor is it individually eligible for listing in the National Register of Historic Places. The National Historic Preservation Act (NHPA) Section 106 review for the project resulted in a No Adverse Effect finding for the Chestnut Hill Historic District.

Inspection and Emergency Repairs

Prior to 1994, the bridge was on a regular five-year inspection cycle, per Federal Highway Administration (FHWA) standards. However, due a metallurgical flaw of the 1962 replacement steel and the constant infiltration of water and snow salts through the asphalt deck, deterioration aggressively accelerated beginning in 1995. Because of this, stabilization repairs were required, and inspection reporting was increased to a two-year inspection cycle. For the repairs, the City’s Bridge Section performed in-depth inspections to develop rehabilitation and reconstruction strategies. The major findings were as follows:

1. Severely corroded steel, including the pier steel bent frames.
2. Seized and malfunctioning bearings and expansion dams.
3. Abutment and wingwall stonework in need of repointing and/or rebuilding.
4. Moderate spalling of the drivable asphalt deck surfaces.
5. Failure of the superstructure steel coating system.
6. Moderate deterioration of the non-composite deck stay-in-place forms.

Due to severe steel deterioration under the sidewalk bays, elevated wood boardwalks were furnished and installed temporarily by the City’s Bridge Maintenance Unit in 2006 to bridge over weakened areas and to provide safe passage of pedestrians. Concrete median barriers were also installed at the curb lines to keep vehicles off the sidewalk. Figure 1 depicts these changes. Additionally, a truck detour was instituted around the bridge to remain in effect until full reconstruction could take place.

In 2013, the condition and section loss of the stringers, as shown in Figure 2, became so significant that another emergency repair was done. Additional adjacent “buddy beams” were furnished and installed by Buckley Construction Company to strengthen the weakened stringers. This system is shown in Figure 3. This would allow the bridge to remain in service for one more winter season without closure and impact to the commuter rail traffic below.

At this point, the structure became the primary design priority for the City’s design unit. Due to deterioration and/or section loss of up to 100% in some places, permanent bridge closure was imminent. The bridge was posted for 3 Tons/No Trucks. At the time of last inspection the structure’s sufficiency rating had reduced to 2.

 

Design

The design scope included removal and replacement of the entire superstructure, substructure strengthening/adaptive reuse, roadway approach work, reconstruction of a portion of train station platform stairway, and utility work. The engineering and logistical challenges involved with replacing a severely deteriorated, weight posted, structurally deficient bridge that is also integrated into an existing SEPTA commuter rail station were apparent. Moreover, very little information by way of existing plans was available, necessitating extensive survey and substructure probing to verify project conditions. Prior to construction, Verizon, Comcast, Street Lighting, and Philadelphia Electric Company (PECO) facilities were relocated, and SEPTA Electrical Traction power cables at the west pier were detached. Work would be done in shifts, when required, and would be coordinated with SEPTA, Verizon, Philadelphia Water Department (PWD), and Philadelphia Gas Works (PGW).

Due to the uniqueness and historic setting of this bridge, the design team faced numerous challenges, apart from typical design challenges in a densely populated environment. One of the key questions that had to be answered early on was if the existing substructure could be reused for a third time. Salvaging the substructure was desirable because it would exhibit sustainability, reduce environmental impact, and lessen construction cost. Michael Baker International was contracted as part of the design team with two main substructure tasks: verify the existing substructure conditions and design an adaptive re-use.

In order to preserve the existing horizontal clearance of the rail, the existing stone masonry piers were maintained. The existing pier foundations consisted of open joint masonry stone walls founded on stepped stone footing. These existing foundations were strengthened by placing a 1’-0” thick Class C concrete collar around the perimeter to lock in the foundation and solidify the foundation for reuse, as shown in Figure 4. The existing stone masonry piers were cleaned and entirely repointed, and a new concrete cap was attached to the existing cap in order to support new HP12x84 steel columns. The concrete collar was placed over several track outages with high early strength concrete, which allowed for live rail traffic within 1’-0” of the collar placement at the end of each outage.

To stabilize the existing abutments and wing walls, existing backfill was carefully removed to the bottom of the existing walls and replaced with Class A concrete immediately behind the masonry structure to form a new gravity abutment. This concept knits the “old” structure and “new” structure together. This was done while the existing walls were monitored for excessive movement. The stone masonry of the abutments and wing walls were cleaned and new caps were provided on each abutment to serve as a beam seat. To eliminate earth pressure acting on the gravity abutment and wing walls, Class C concrete and flowable fill were placed behind the Class A concrete in lifts approximately 3’ wide and 2’ high. These abutment stabilization measures are shown in Figure 5.

After the substructure modification, stringer design began. Numerous beam design runs were performed and compared to the limited available superstructure depth envelope. The City opted against the use of plate girders in this application due to cost and fabrication issues for such shallow members. Additionally, it had committed to provide at least three more inches of vertical clearance over the electrified railroad. Still, a PUC design exception for substandard vertical railroad clearance was required.

The design scheme mimicked the existing configuration of very shallow, closely spaced stringers. The City design team would improve on the existing structure by converting the arrangement to a three span continuous structure, thereby creating a more favorable load distribution. Twelve inch deep, rolled sections were proposed, except for at the fascias, where deeper rolled sections were planned. Additional live load deflection calculations were required to gain PennDOT approval for this design scheme. The design team also had to demonstrate that cambering could be done for such a shallow rolled section, held down at four points. Cambering feasibility was verified by recognized fabricators in the region who noted that the cold cambering method could be successfully implemented in this case.

Shallow depth rolled sections could meet the existing envelope for the cartway, but left the challenge of fitting three utilities within two sidewalk bays. Further complication arose due to the fact that the north bay would feature two liquid utilities – an 8-inch PWD water main in a 16-inch casing pipe and a 4-inch PGW low-pressure gas main in an 8-inch casing pipe, as shown in Figure 6. Both utility lines would require larger diameter casings for safety and installation purposes. To satisfy the local community organizations, Section 106 consulting parties, and the Philadelphia Art Commission, the design team opted to cleverly hide the utilities within each sidewalk bay. This would require two different curb reveal depths and an atypical deck cross-section.

The deck did not extend transversely to the edge of the sidewalk, as is typical. Instead, the deck was discontinued just below the curb line. This allowed sufficient room for the utilities to sit beneath the sidewalk, while maintaining the railroad clearance below, though the north curb reveal would still have to be nearly twelve inches deep to fit the PWD and PGW mains. Though unusual, this increased curb reveal proved to be subtle and hardly noticeable. The sidewalk slab would be just six inches thick and not cast on a deck slab. This minimal thickness required special calculation to ensure that the sidewalk could support typical live loads. Two rebar mats were still required, but the position of the bars was slightly altered to accommodate all applicable covers.

To facilitate utility installation and maintenance and to avoid the issue of future sidewalk settling at the bridge corners, the approach sidewalks were designed integral with the approach slab. Unlike the deck slab, the approach slab would be full width, out to out. Strip seals would be placed on sleeper slabs at the far ends of the approach slabs to meet current PennDOT design criteria. At the east approach, the sleeper slab and strip seal would need to be adjusted to work around a new stairway foundation block designed for the SEPTA commuter train station.

A study revealed the need to improve safety at the four corners of the bridge by providing guiderail. However, guiderail is considered to be unsightly by the public, so the team searched for an appropriate design solution. All four corners featured slopes with various degrees of inclination. In order to minimize impact to the existing slope and tree root systems, the team decided to design the shallowest possible foundations to support the guiderail. This would be accomplished by utilizing moment slab with a tapered foundation. The design feature would also lower construction costs and minimize disruption to the adjacent property owners, while allowing for all work to occur within the narrow City-owned right-of-way. At the southeast corner, a thickened edge of sidewalk would be utilized to span over well-established evergreen trees. An example of this is shown in Figure 7. The design team had committed to protecting the root systems of these trees, such that all would survive during construction. Protection would come in the form of special design details and coordination with the City arborist.

The design team settled on a shallow depth, crash tested Virginia DOT barrier system that would sit atop a shallow depth parapet. This arrangement was amenable to all parties involved and would allow the bridge architect flexibility in design. The parapet would later be widened to 1’-6” to accommodate real Wissahickon stone veneer, inset on both sides. Additionally, the steel barrier was modified by the architect with decorative balusters. Neither alteration would lessen the crashworthiness of the assembly.

Several other safety improvements were incorporated into the structure, including matching the original cartway width of 28 feet, striping 10.5 foot wide lanes in lieu of 12 foot, and providing 3.5 foot-wide colored shoulders. The striping and coloring were intended as traffic calming measures to improve safety.

The project design requirements would dictate the use of a steel protective railroad barrier, in lieu of standard aluminum. Three possible designs were presented to the community and Philadelphia Art Commission, as well as the Section 106 consulting parties. The barrier chosen was modeled after the nearby railroad bridge at Springfield Avenue and would feature the name of the adjacent SEPTA station, St. Martins, on both sides. All fasteners would have decorative rivet heads, in keeping with design details of the original structure.

As mentioned previously, the moment slabs would feature real inset stone veneer, and this decorative element would be extended to the bridge parapets as well. Research was done regarding the tooling of the joints, as well as for the correct mortar mix design. The construction requirements were specified in accordance with the National Park Service Guidelines, and sample panels were provided at the community input and pre-construction stages of the project. Lastly, all future veneer and restoration of the existing stone walls would have the same mortar details.

For the approaches, extensive coordination with each property owner was required. Where tree removal was necessary, owners were given the option to have trees removed or replaced. Additionally, existing slate sidewalk could be replaced in kind or replaced with pigmented concrete. Concrete would cost less and provide greater design flexibility, especially for ADA ramps, while using slate would preserve the historic construction materials and methods.

Of course, many other historic requirements had to be met due to the bridge’s location in the Chestnut Hill Historic District. For instance, rivets were used in the existing barrier ironwork that was removed, so the barriers had to be replaced with an historic-looking bolt. The bolts chosen included rounded rivets at both ends. The actual bolt head featured a twist-off mechanism – set to go off when a certain torque was achieved by the ironworker. Historic-looking punch rivets were also used for the handrail; when hammered into place, the rivet head went smooth and expanded the bolt to secure the railing.

Construction

The project also included many interesting construction challenges which the City’ Construction Unit and the contractor, Loftus Construction Company, worked through together. One of the biggest challenges was constructing a bridge over an active operating railroad. Though only the middle span was over active tracks, the bridge’s entire footprint had overlapping Right-of-Way with SEPTA. Much of the work over the tracks could only occur during track and power outages, which could occur at night and last just three to four hours on average. Many outages and night crews would be needed to get through the demolition and deck reconstruction phases of the project.

Because the bridge was in very poor condition, contract documents included weight restrictions and equipment placement limitations. This challenged the contractor to devise creative means and methods for construction, mainly utilizing small equipment.

Abutment wall stabilization proved to be a challenge in the field due to the variability in shape of the existing stone. The doweling pattern, location, and number specified in the plans had to be modified to maintain the integrity of the existing masonry wall. Therefore, holes were placed at existing gaps between the dry-stacked masonry, trying to match the specified number and location of dowels as closely as possible.

Due to the shallow interior beams and presence of utilities in the fascia bays, standard diaphragms could not be utilized. Therefore, the utility supports functioned as braces between the girders. However, the location of the utility supports fell on the bottom portion of the fascia girder, which left the top portion of the fascia girder unbraced. This caused stability issues for the fascia girder during construction due to the exterior overhang support system.

To prevent excessive overturning force on the exterior girder, WT sections were bolted to the top of the interior girder at regular intervals. Double angles were then extended between the WT section and the exterior girder to provide sufficient bracing to allow construction operations, as shown in Figure 8.

The profile of the PWD water main would become an issue where the end bridge span transitioned to the approach slab. In particular, the steep roadway grades for the crest curve exceeded the standard limitations of standard pipe and pipe casing deflection joints. In this instance, custom length pipe sections were needed to meet the main profile.

The change in the proposed vertical profile of the bridge affected the private driveways at each end of the bridge. These already steep driveways were subject to increases of over 12 inches in some cases. Therefore, each driveway required a small sag curve for adjustment purposes. Additionally, portions of original Belgian block drainage swales were rebuilt on either side of the driveway.

Summary

Though the rehabilitation of the Willow Grove Avenue Bridge over SEPTA was complex and challenging in both design and construction, the project was a sound investment in this Chestnut Hill Philadelphia neighborhood for many reasons. The project appropriately restored a bridge, fitting it properly to the area’s historical context, and set the standard for future projects in historic areas. This exercise was lauded as an excellent example of context sensitive design by the community and critics alike. The most direct route through the neighborhood was restored, improving the flow of traffic and accessibility for EMS vehicles. The extensive use of in-house engineering excellence and consultant support services helped restore grandeur and functionality to the very deserving structure shown in its completion in Figure 9 (Track Level) and Figure 10 (Street Level).

 

IBC – 08-75

Acknowledgements

City of Philadelphia Streets Department Surveys, Design, and Construction Unit/Bridge Section

Darin Gatti, P.E – Chief Engineer

William Gural, P.E. – Chief Construction Engineer

Vadim Fleysh, P.E. – Chief Design Engineer

Christopher Menna, P.E. – Engineer of Design

Dhanya Jacob – Project Engineer

Timothy Dragan, E.I.T. – Project Engineer

Tyler Barile, E.I.T. – Resident Inspector

Richele Dillard – Lead Draftsperson/Designer

KSK, Philadelphia, PA – Bridge Architecture

Michael Baker International, Philadelphia, PA – Substructure

SYSTRA, Philadelphia, PA – ET Design

AD Marble, Conshohocken, PA and CH Planning, Philadelphia, PA – Cultural Resources Support

AECOM, Philadelphia, PA – Contract Management Support

Jacobs Engineering Group, Philadelphia, PA – Construction Support

General Contractor

Loftus Construction Co., Cinnaminson, NJ

Agencies

PennDOT 6-0

SEPTA

FHWA

Rebecca A. Bowman, Esq., PE

One of the most important general skills for a business owner is the ability to plan ahead. What that really means is the capacity to anticipate future events.  One of the important things that all we engineers can reasonably anticipate is being called upon to defend our work.

One component of defending our work, whether in negotiation, a deposition, arbitration, or court, is documenting evidence of our competence. Whether you call the documentation a resume or curriculum vitae, you should have it ready at the drop of a hat. For ease of discussion, I’m going to refer to the document as a resume.

Now, your mother probably taught you that it’s not nice to brag on yourself (to use a quaint Pennsylvania expression). That’s usually true. Nice people let others brag on them. However, that is not always true, and this is an example of when it’s not true.

Just in case you were worried, having your resume ready is not a sign is disloyalty to your employer or your business. It is not a sign or signal that you’re restless and looking for a new opportunity. It is a sign of your wisdom in anticipating the need.

Furthermore, marshaling some of the information you should have on your resume isn’t always easy to do on the spot. If you taught a professional development class three years ago, can you produce the date, topic, sponsor, and location? This instant? Probably not. However, if you maintain a resume at all times and update it with each new accomplishment, you won’t have to scramble.

With the current Pennsylvania law regarding professional development, you should have information like that gathered already for your license. However, that file may be a paper file (with certificates attached, of course) and not an electronic file, so you may not be able to access it on the fly.

Companies come and go. Several times in the past few years, I have had to assist engineers in reconstructing information about their former employment because the company was gone and they didn’t have the necessary reference information for their resumes. If you maintain a resume, you won’t have that problem.

Now, if you’ve been around the block several times as I have, your base document may be many pages long. I maintain a base document that includes every assignment I have ever had, every article I have ever written, every lecture I have ever taught, and every case for which I appeared as an expert. When I need a resume to support my status as an expert, I go into that base document and select examples relevant to the situation. In general, a resume to support your qualifications should not be more than four pages long. You can summarize data. For example, “I have appeared as a boundary expert in 26 cases in Pennsylvania, 14 in Ohio, and 6 in Federal courts” is a useful summary sentence. If someone challenges that qualification, you need to be able to document those cases, but you don’t need to list them. One exception would be a situation in which your testimony resulted in a change in the common law (pattern of decisions established by cases, not legislation). That would be something to celebrate separately. I typically show interesting work in the past five years and summarize what came before, unless it’s something special.

If you think that I’m exaggerating the importance of this preparation, I was a part of one case in which the expert (not I) was being challenged. The challenging attorney had subpoenaed the expert’s Professional Engineering licensing exam. Waving that exam, the challenging attorney tried to argue that the expert was not an expert in the particular field because he had not selected the exams questions in that field for his responses (i.e. he answered the soil questions and not the water questions). The attempt to disqualify him failed, but it was a shocking example of how deep the opposition may dig.

Lest you think that I am not consistent, I tell the students whom I mentor that they should start to gather this information with the first (non-participation) award they receive, even if that is in third grade. On applications, colleges want to see that a student has been consistent in participation or shown a pattern of academic activities, a pattern of success. As with we grow-ups, that information can be hard to gather after the fact. And most scholarship applications require some sort of resume.

Even if you think that you will never be called to appear before a fact-finder, you may want to apply to graduate school or for some program for which you need to demonstrate that you have fulfilled the pre-requisites. Again, you may not be able to scramble to gather the necessary information.

If you consistently maintain your resume, you will always be ready. Otherwise, you may be putting yourself in a Risky Business.