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Support Under Distress

 

The 6.0 magnitude Napa Earthquake struck on August 24, 2014,  and caused substantial damage to many structures in this popular tourist destination.  DHC received many calls during the aftermath of the earthquake, as the damage was widespread and structures were in need of temporary support.  Bracing and shoring was deemed necessary for many building simply to allow personnel to gain access, retrieve belongings, or survey the true extent of the destruction.

One building that was hit particularly hard was the Historic Napa Courthouse located downtown on Brown Street.  D.H. Charles Engineering, Inc. was contracted to develop a wall bracing system that could be installed without positive anchorage to the wall itself.  This was imperative, as the competence of the wall was unknown and workers could not be exposed to a potential collapse during bracing installation.  The resulting system consisted of vertical I-beams that were rotated upwards against the wall, and then diagonally braced with tilt-up braces anchored to the wood floor joists.  This scheme and installation process provided the necessary safe working environment, and ultimately allowed for temporary scaffold towers to be placed inside the room which provided temporary support to the roof.

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DHC was also contacted by RMB Management Company to come up with a solution to recover personal items for customers of the heavily damaged two-story self-storage building at the Napa Self Storage facility.  The entire second story had  shifted out of alignment from its foundation such that the first story walls were heavily skewed and damaged.  The primary challenge was not being able to visibly see the full extent of the damage without first stabilizing the whole building and providing safe access to the structure.

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Our first step was to design an exterior bracing system at the second floor, for global stabilization, and relieve load to the damaged interior walls.  We then designed an extensive plan to incrementally provide internal access to the lower floor units.  Modular scaffold shoring would be used throughout the building’s access points to simultaneously shore the lower level while providing safe entry for workers to evaluate the extent of the damage, recover personal belongings, and provide additional shoring within the storage units as necessary to stabilize the structure.

DHC enjoyed the opportunity to support their neighbors in a time of need, and help the residents and businesses of Napa return to normal life.

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DHC Expands to Seattle Area

After much planning and the steady encouragement of many of our customers, DHC is proud to announce the opening of an office in the greater Seattle area.  With main branches in Santa Rosa & San Diego, and satellite offices in Oakland & Sacramento, the Seattle location becomes the 5th for DHC.

This new office is being managed by John Meissner, PE, who is a native of the Pacific Northwest and is excited about the opportunity to meet with many customers personally in coming months.

Even without local branches, DHC has maintained a tradition of effectively servicing contractors throughout the US and Canada, and has developed long-lasting relationships with many of them.  Nonetheless, we look forward to the opportunity to meet many new and existing customers in person, and plan to host various training programs and introductory meetings in the coming months and years.

If you would like to learn more about DHC, or to meet in person, please do not hesitate to contact John Meissner, President Jasper Calcara, or General Manager Luke Griffis.

Partial List of Engineering Services Provided:

  • Excavation Shoring/Safety
  • Tunneling and Boring
  • Scaffold Structures
  • Bridge Jacking and Support
  • Suspended Platforms
  • Crane and Rigging
  • False/Formwork
  • Structural Shoring
  • Re-shore
  • Fall Protection
  • Rebar Cage Stabilization
  • Containment Design

 

 

 

 

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Industry Leader – Guest Lecturer – UCSD

D.H. Charles Engineering, Inc. (DHC) was invited to be a guest lecturer for roughly 120 graduating seniors of the University of California San Diego (UCSD) Structural Engineering department.  With an established passion for educating the construction industry in engineering challenges and safety, DHC was more than happy to accept the invitation, and had the perfect candidate to send to the classroom.

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Chong Kim, P.E., a senior engineer and alumni of the same program at UCSD, has worked on thousands of construction engineering designs throughout the US and Canada in his career at DHC.  He took that experience on a wide variety of projects, and developed a presentation titled Temporary Structures and Construction Engineering Industry, to present to students taking the SE140 course.

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SE140: Structures and Materials Laboratory, introduces students to real world challenges and applications of structure design, including: Problem formulation, concept design, configuration design, project management, team working, ethics, and human factors.  –UCSD Course Curriculum

The variety of situations and challenges faced on a construction site can be overwhelming, with many codes and design approaches never discussed at the University.  Therefore, the presentation narrowed the field of construction engineering and focused in on the following key areas:

  • Excavation Shoring
  • Construction Slopes
  • and Slope Stability Analysis
  • Tunneling and Boring
  • Scaffold Structures
  • Bridge Jacking and Support
  • Suspended Platforms
  • Crane and Rigging
  • False/Formwork
  • Structural Shoring
  • Re-shore
  • Fall Protection
  • Rebar Cage Stabilization

Most students do not have the real-world experiences that come with time and that are hard to find in text books, so it was important to illustrate each subject area with as much photographs, colorful anecdotes, and challenges that were faced on particular projects.

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It was important to Chong that he connected with the students on a personal level, as he could clearly recall sitting in their position all those years ago.  He focused on the challenges and fears all young professional faces when starting their first jobs, as well as how to evolve as the their careers take them in different directions.  But most importantly, he wanted to exemplify how important it is to continue to take on challenges and overcome their professional and personal fears.  Presenting in front of peers was a first for Chong, and something he was very proud of accomplishing.

There were many insightful questions from students throughout the presentation, showing that they were truly interested in and engrossed with the subject matter.  The open discussions covered many aspects of construction engineering, codes, loads, workplace environment, as well as general challenges facing engineers in today’s world.

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Evoking passion for what we do as engineers is the most important thing an educator can do, and based on the enthusiasm and response of the students, we are hopeful we were able to accomplish this.  We want to extend a special thank you to Professor Lelli Van Den Einde, Ph.D. for bringing us into her classroom and organizing the guest lecturer opportunity, and wish the best of luck to the class of 2016!

 

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Engineering Solutions – Enclosed Scaffold on High Profile Bridges

Enclosed scaffold systems on bridges can expose some of the most complex erection and engineering challenges to face the scaffold industry today.  Extreme heights, elaborate bridge profiles, severe wind speeds and other complications regularly drive scaffold contractors and engineers to develop state-of-the-art solutions.  The following three high-profile bridge projects may have faced similar design obstacles, but ultimately they each implemented unique and individually successful solutions.

Dames Point Bridge – FL

Dames Point Bridge, FL Project

Abhe & Svoboda, Inc. (ASI) was faced with the daunting task of providing full access and enclosure of all stay cables on the Dames Point Bridge in northern Florida.  With scaffold heights pushing 300 feet, D.H. Charles Engineering, Inc. (DHC) worked closely with ASI and bridge engineers to develop an enclosure and wind speed removal scheme which would allow for completion of painting operations, while ensuring that scaffold and bridge components would not be overloaded.  After completion of preliminary engineering, the system was eventually designed and certified to withstand 40 mph wind speeds when enclosed with shrink wrap, and 131 mph wind speeds with the enclosure material removed.

The primary challenge was proving that the 7-foot wide scaffold, being secured to only the bridge suspension cables, could reach the tremendous heights without overstressing scaffold elements or exceeding the capacity of bridge stay cables.  Stresses in the scaffold members were directly related to how much the framework would actually move horizontally under wind load.  On most projects the scaffold is tied uniformly to rigid support elements so that the entire scaffold exhibits minimal deflection between unyielding tie points.  In this case, the supports themselves, the stay cables, varied in length up to 700 feet and each point on each cable was able to move a different distance under the same load.  Due to this complication and the non-uniform geometry of the bridge, a simplified linear design approach was ruled out.  Ultimately, a complete 3D model of the entire scaffold system was developed, accounting for the different rigidity of each and every cable stay tie point.  Vertical diagonal bracing and anchorage to the bridge were then strategically placed, in order to finalize the design and confirm adequacy of the overall system.

The work was completed successfully, but not before the entire system and engineering was put to the test by Mother Nature.  Original weather reports had Tropical Storm Fay projected to completely miss the project site.  However, a last minute shift in direction brought the storm to the scaffold before ASI could completely remove the enclosure material as directed by the design plans.  Scaffold workers rushed to make large X-cuts throughout the shrink wrap in order to increase wind flow through the enclosure and reduce impact on the scaffold.  Although the enclosure material completely disintegrated due wind speeds in excess of 80 mph, there was essentially no damage to the scaffold itself, and the project was completed on schedule.

San Francisco-Oakland Bay Bridge – CA

San Francisco-Oakland Bay Bridge Renovation – CA

As construction wraps up on the high profile east span replacement, it not as widely known that the west suspension span of the Bay Bridge underwent a significant seismic retrofit not too long ago.  To complete a portion of this work, the roughly 460 foot tall main towers were enclosed with an access scaffold and containment system over their entire height, in two phases.  Unlike the Dames Point Bridge, this system was designed for maximum anticipated wind speeds, with no plans to remove the enclosure material.  Although dealing with very high leg loads and other design issues proved difficult, it was the containment and geometry of the bridge tower legs that resulted in most of the complications during the design phase.

The diamond shaped voids between the tower bracing resulted in horizontal and vertical gaps of up to 60 feet between available tie points.  The independent scaffold walkways did not prove adequate to allow the scaffold to free span these gaps.  Therefore, plan bracing and horizontal ties were used so that the entire scaffold cross section shown below could be analyzed as a giant truss with each walkway acting as either the tension or compression chord, depending on wind direction.

Using the geometry of the tower legs to our advantage, we were able to brace the scaffold chords tight to the tower steel in multiple directions, and transmit the high loads over long spans with a light and very efficient framework of scaffold.  Preliminary analysis showed that extreme axial loads would develop in horizontal tubes of the compression chord, and overload many of the members.  However, the flexibility of modular scaffold allowed for multiple options to resolve this problem.  One solution included placing truss ledgers at locations of maximum load to increase strength of the individual framing, while another was to simply install ledgers at every cup along the height of the scaffold to spread the load to multiple tubes.  Use of systems scaffold also allowed for the cross section of the entire scaffold tower to be easily tapered as the tower reduced in size over its height.  This scaffold was ultimately erected at multiple locations throughout the scope of the project, and performed exceptionally well.

Golden Gate Bridge – San Francisco, CA

When performing a state of the art retrofit on one of the most beloved bridges in the world, contractors were forced to extreme measures to perform their work without impacting the integrity of the structure.  At the south approach of the Golden Gate Bridge, a roughly 300 foot arch gracefully bows over the civil war fort below.  This popular tourist destination was built in the 1850’s, and was to remain open to the public during the extensive work above.  Suspended platforms, complex scaffold and extensive containment systems were widely used to allow for work throughout the arch.  The most complicated of the many systems designed for Shimmick Obayshi, included a 200 foot tall cuplok scaffold system, partially supported by a suspended aluminum space frame platform, and completely enclosed with shrink wrap.

The bridge district required that every structural element of the existing arch be checked for the loads to be imposed upon it from the scaffold system, in conjunction with original bridge design loading.  Therefore, DHC had to demonstrate that elements originally exposed to wind pressures across their 2 foot width could now support wind from a 36 foot wide sail.  Normally, a very dense scaffold system, or possibly an external bracing scheme would be implemented to help relive the structure from the increased loads.  However, due to restrictions from the fort below, and limited access in general, a very minimal framework of scaffold would be allowed.  Therefore, an intricate hybrid system of cables, scaffold and suspended platforms was ultimately developed to satisfy the bridge’s enclosure needs

Numerous 7 foot by 10 foot systems scaffold towers were erected around the main arch columns, which free spanned up to 70 feet vertically and were spaced as far apart as 42 feet 6 inches on center.  This scaffold was either directly supported from the ground, or set on an independently suspended work platform.  These individual scaffold bays were then tied together with a matrix of cables, which acted as the supporting skeleton of the shrink wrap.  These cables were installed with very specific sags between the support points at each scaffold tower, in order to control the high tension loads that would develop, and attempt to pull the opposing scaffold together.

Golden Gate Bridge - San Francisco, CA scaffolding plans

The cabling proved to be the backbone of the entire scheme, allowing for a light and efficient overall system while providing the vast enclosure required for the work site.  Although the cabling was efficient from an installation point of view, it proved to be challenging on the engineering, as the cables developed extreme tension loads which were passed to the highly taxed bridge elements.  Eventually, by simultaneously manipulating the cable sizes, spacing, sag, scaffold assembly and wind speeds a system was chosen which met everyone’s needs and gained approval from the bridge district.

With the overwhelming magnitude of the project, elaborate site restrictions and endless field changes, it was truly impressive that a scaffold implementing so many complex support, bracing and reinforcing schemes could work in harmony to meet the demands of this world class bridge.

Year in and year out, our nation’s most historic and important bridges require extensive repair, maintenance, and retrofit work.  The scaffold industry has played a vital role in allowing this work to be completed efficiently and safely while being exposed to some of the most hazardous conditions in the construction world today.  Pushing the engineering and erection envelope has allowed scaffold contractors to stay at the forefront of this industry, has exhibited in some of the most impressive projects over recent years, and leaves us excited to see what the future brings.

Ballard Drive Bridge Engineering Project

SAIA – Balancing Needs – A Bascule Bridge Story

Published in the September 2012 issue of SAIA

By Jasper Calcara, PE

If you can imagine the risks of two sumo wrestlers jumping on a child’s seesaw, you can start to visualize the challenges facing engineers on the Ballard Drive Bridge painting project.

The Ballard Drive Bridge is just one of many historic bridges scattered throughout the Pacific Northwest, which has maintained regular service for nearly 100 years.  Due to their age, continuous use, and exposure to the elements, these bridges require regular inspection, maintenance, and repainting.  Performance of this work can often result in difficult challenges for specialty bridge and painting contractors to provide efficient, safe, and contained access.

Ballard Drive Bridge Engineering ProjectThe 218’ span double-leaf bascule bridge was one of four bascule bridges built in Seattle between 1917 and 1925, and acts as a critical artery for local roadway and boat traffic.

It was added to the National Register of Historic Places in 1982, and uses a system of finely tuned counterweights and machinery to raise the bridge to near vertical.

Purcell Painting & Coatings, was contracted to blast and paint the entire structure, and contain all the lead paint debris, without restricting operations of the bridge. Raising the bridge anywhere from 250 to 500 times a month prohibited dismantling and reinstalling the access system each time, and therefore the platform would have to rise with the bridge.

Raising the platform presented extreme challenges to the design team, as the suspended deck and bridge structure would be exposed to complex loading conditions not normally experienced by a traditional horizontal platform.  Intense wind loading on the underside of the platform, stabilization during raising, analysis of all bridge framing, as well as very sensitive counterweight restrictions were only a few of the issues to be resolved.

After working with multiple engineering groups who were unable to devise a suitable solution, Purcell decided to proceed with the system proposed by D.H. Charles Engineering.  President Jasper Calcara, PE and suspended platform design engineer Josh Rubero, PE outlined a Safespan suspended platform and staged containment program, which would allow for full erection, stabilization, and containment within all bridge limitations.  The key to the design was the use of extremely light decking, as every pound of platform added to the bridge had to be carefully counterbalanced within strict limitations.

The platform loading and added counterbalance proved to be the sumo wrestlers on the seesaw, wanting to overload the bridge if too much weight was added to each side of the pivot point.  It was such a critical issue that a city engineer was on site throughout the duration of the project, carefully monitoring the addition and removal of over 900 pieces of 50 lb. counterweights strategically placed in accordance with the design plans. With the loading limits satisfied, the stability of the platform and strength analysis of the bridge framing had to be resolved.

Ballard Drive Bridge Engineering ProjectThe Safespan platform consists of corrugated steel decking, longitudinal support cables and vertical suspension devices, which result in a very flexible overall system.  Although the deck is very light, it lacks the critical rigidity that a typical scaffold or suspended platform system provides.  Unfortunately, it was the weight of more rigid systems that made them impossible to utilize, and engineers were faced with the task of stabilizing a system that would turn into a nearly 4,500 square foot flexible wind sail.

When the platform rotated to near vertical, engineers were concerned with high winds hitting the exposed face of the decking and slamming it into the underside of the bridge, while gravity attempted to shift the deck out of position.  Therefore, a series of rigid anti-uplift and horizontal bracing members were installed to hold the deck firmly in place, while intentionally passing the load to the stronger framing points of the bridge substructure.  Lastly, an array of vertical to horizontal suspension cables were devised to allow the platform to shift orientation, and eliminate any sag or sway of the deck toward the water.

Although the structural evaluation of the bridge and platform design were extremely extensive, the final product functioned perfectly throughout the duration of the project.  The entire system proved safe and stable, requiring very little modification or maintenance as the job proceeded. Even with rain on 70% of the workdays, there were no breeches of the containment system, and the job finished on schedule and within budget.

The careful consideration and evaluation of all the potential risks, as well as close collaboration between the contractor, engineers and city representatives, were critical to the completion of this project. With another innovative solution executed with precision, the industry is that much more prepared for the next challenge to be presented.