Working Wonders With Wood

St. Mary's Church Renovations

2011-12-02T09:24:00.000-08:00

The historic St. Mary’s Catholic Church in Mt. Angel, Oregon was dedicated in 1912. The 50’ tall steeple that was perched above the bell tower was constructed from wood and the heavy timbers that formed the main outside supports were lap-jointed and bolted together to achieve the required length.

Water spotting on the ceiling was discovered during the Fall of 2010 by church members but it wasn’t until a severe Oregon rain storm during the following winter that the water damage grew enough to cause plaster to fall from the ornate ceiling.

Realizing that something had to be done, the Church turned to Schommer & Sons Construction of Portland to perform a thorough inspection and make repair recommendations. Schommer’s initial inspection showed that water was leaking into the structure through several places including openings in the steeple’s copper sheathing which resulted in significant decay to the steeple’s timber framework.

Schommer & Sons then employed the services of Conley Engineering, Inc. who concurred with Schommer’s initial inspection and designed the needed structural repairs.

In front of a large gathering of interested community members, the steeple was cut loose from its support beams and lowered to the ground with a crane. It was first believed that the steeple could be repaired but after a more thorough inspection the decision was made to replace the steeple due to the extent of the damage and the cost of repairs.

Western Wood Structures was then hired to design, fabricate, and deliver a new steeple. The Heavy Timber steeple, which measures 50’ in length and just over 12’ across at the base, was fabricated and assembled in our shop. It was constructed of full length Glulam ribs, 4 x 6 struts, and 1-1/8” T & G plywood and trucked to the site on a special “stretch double drop deck” trailer.

Schommer & Sons completed the attachment of the ice and water shield and the installation of the copper cladding in the church parking lot and safely set the new steeple back into place in early October, 2011.

Whistle Stop Trail Bridge

2011-11-09T10:09:00.000-08:00

The Whistle Stop Bridge, currently under construction, is a cooperative venture between the US Forest Service and the Alaska Railroad to make the Alaskan backcountry more accessible. This bridge is located along the Alaska railroad between Portage and Moose Pass, Alaska. The area is accessible to recreationists by a self-propelled rail car. The Glulam Bridge will span 282’ and cross the Placer River and when complete will be the longest clear-span timber bridge in North America.

The USFS solicited proposals and considered several design-build options but settled on a design submitted by Western Wood Structures through Patrick Engineering, a General Contractor from Denver, Colorado. To meet the Forest Service’s preference, the bridge design is a Camelback Truss style which is typical of many bridges built in the early 1900’s.

The bridge was pre-fabricated and trial assembled at our facility prior to pressure treatment. Due to its length, we could only pre-assemble three of the five 56’ sections at a time.

The bridge components were shipped to Anchorage by barge and railed to the site for final assembly. The installation scheme called for assembly to take place on either side of the river. Pinned connections were used in the bottom chord splices to facilitate assembly and erection.

Western Wood Structures furnished a superintendent to assist the Contractor in the truss assembly.

Ultimately, hikers will be able to safely cross the Placer River to access the spectacular Spencer Glacier and not be tempted to use the existing railroad trestle.

Dana Hall Repairs

2011-08-31T08:54:00.000-07:00

Dana Hall, on the campus of SUNY College of Technology in Canton, New York, was constructed in 1969. It was built to accommodate the College’s athletic teams and physical education classes. The main framing consisted of Glulam arch frames spaced at 18’ centers spanning 108’-6”.

About two years after the building was opened, cracks were noticed at the moment splice locations which concerned the owners enough to call for a series of inspections. It was determined that the cracks were not structurally significant as long as they did not propagate but since the cracks were evident in the same location in each of the Glulam frames, this confirmed that an inherent issue existed with the design. It was decided that the splits would be “monitored” to make sure they didn’t progress further.

In 1998 Canton experienced a heavy snow storm. In 2006, maintenance personnel noticed that the cracks had propagated and opened further. Following another inspection, an attempt was made to repair the most heavily split arch frame using lag screws inserted from the bottom of the arch. But new splits occurred after the lag screws were installed near the tops of the new lags so a second attempt was made to close the splits using steel angles and an HSS section to clamp the arches.

These attempts proved unsuccessful so the College began exploring the cost to demolish the building. Initial demolition estimates were in the vicinity of $2.3 million. But before the final decision was made to demolish the building, the College decided to make one final attempt to repair the Glulam frames. An internet search led them to Western Wood Structures who was hired to perform an inspection, complete a structural analysis, and make recommendations for a permanent solution.

The College decided to accept Western Wood’s opinion that the frames could be repaired as well as brought to current code and the decision was then made to advertise the job to the general public on a design-build basis. Western Wood turned in a bid and was eventually awarded the contract for just over $1.1 million.

There were four repair and code upgrade methods used by Western Wood Structures to complete the necessary repairs:

1. The frames were post-tensioned due to being over stressed in bending;

2. Additional laminations were added due to being over stressed in bending;

3. Shear dowels were installed to restore the shear capacity of the members. Some of the holes drilled into the arch frames were 54" deep;

4. Side plates were installed at the moment splice locations to transfer the reaction of the beam to the arch section.

Dana Hall has been saved from the wrecking ball and today, SUNY College of Technology has a multi-use building that will safely serve their needs for many years to come.

Dana Hall Repair White Paper

The Angus Bowmer Theater

2011-07-27T08:23:00.000-07:00

On June 16th of this year, a loud “cracking” sound was heard by crew members rehearsing Shakespeare’s “Measure for Measure” so owners of the 600-seat Angus Bowmer Theater in Ashland, Oregon decided to have the sound checked out. Using a catwalk for access, a crew member discovered a large crack in the main Glulam carrying beam above the stage so the decision was made to evacuate the building. The following day, an Ashland City engineer examined the beam and declared the building unsafe for public usage. Alternate plans were then adopted by the Oregon Shakespeare Festival (OSF) so the show could go on.

Adroit Construction of Ashland was hired to shore the massive 14.5” x 78” x 70’ Glulam. Once the shoring was in place, the roof was secure. OSF then hired two engineering firms, Marquess & Associates of Medford and KPFF of Portland, to study the problem and three emergency repair options were considered. In the end, a proposal from Western Wood Structures to design and implement a repair scheme was accepted. Our design was preferred because it did not add a significant amount of weight to the existing roof structure and because the work could be completed in a timely manner.

The Glulam had been split so badly that it was functioning as two small beams rather than one large one. With shoring towers in place, Adroit Construction successfully jacked the beam back to its original position and closed the crack. Western Wood Structures arrived on site July 5th to begin the repairs.

Our first task was to seal the outer surfaces of the beam with an epoxy paste to prevent epoxy leaking. After roofing was removed to allow access to the top of the beam, we then drilled 180 holes into the beam which measured 1-3/8” in diameter and approximately 66” in depth. One inch diameter rebars were placed in the holes and then filled with epoxy, 105 gallons total. Once the epoxy cured, the “shear dowels” had essentially “stitched” the beam back together.

Finally, the beam was post tensioned using steel cable anchors, a steel cable guide, and 15 high strength cables in order to increase its carrying capacity and to meet current code requirements. The cable anchors were installed to the soffit of the beam also using rebars set in epoxy-filled holes.

In our review, we determined that the cause of the failure was attributed to a connection detail on the original drawings. 9” x 32.5” Glulam purlins that measure framing in to one side of the failed beam were attached in hangers near the bottom of the main beam and below its neutral axis which can cause excessive tension perpendicular to grain stresses in the member. Current timber construction standards identify this as a connection detail to avoid.

Our work was completed on July 17th several days ahead of schedule. OSF has announced that the Bowmer will re-open on August 2nd. The owners and Shakespeare fans can rest assured knowing the next play will be performed beneath a main carrying beam that is stronger today than it was when originally manufactured in 1969.

America's Car Museum

2011-06-28T11:09:00.000-07:00

This beautiful timber building, designed to meet the requirements of Heavy Timber Construction, is currently being built in Tacoma, WA. and is scheduled for opening in May 2012. The 165,000 sq. ft. four-story museum will house vintage cars, many of which were collected and owned by Harold LeMay, who owned a succesful refuse company in Tacoma. Mr. LeMay amassed the world’s largest private collection of cars.

Western Wood Structures supplied and installed this unique Glulam roof system and also has design responsibilities for the roof structure. The timber roof framing took about 3 months to install. The museum is being built on land donated by the city of Tacoma adjacent to the Tacoma Dome, another Western Wood Structures project.

The museum is dedicated to the preservation of automotive history and will be utilized for special events such as weddings and corporate meetings and conferences. It will also feature the availability of banquet facilities as well as an outdoor field for festivals and concerts.

Central Lutheran Church Steeple

2011-05-24T10:25:00.000-07:00

Upon completion of renovations to their church in 2005, members of the Central Lutheran Church in Northeast Portland discovered that their Glulam steeple and cross had rotted. A decision was made to tear the structure down due to a lack of funds and liability concerns should the structure collapse.

But the city of Portland had named the Pietro Belluschi designed building a historic landmark in 1970 and city officials informed the congregation that they would have to replace the landmark steeple or face heavy fines. Furthermore, the tower and cross had to look exactly like the original one.

The tower was fabricated, stained, and pre-assembled in four large sections at the Western Wood Structures facility in Tualatin and trucked to the site for final assembly. The City allowed a few allowances because of current building codes but the cross and steeple are very close in appearance to the original.

Three years after the original steeple had been taken down, the new one was lifted into place with two cranes and can be spotted looming 100 feet above the sidewalk in its original position.

Gallatin Field Terminal Expansion

2011-04-14T09:40:00.000-07:00

Construction of the new terminal at Bozeman Gallatin Field is well under way and is on schedule for completion this summer. This expansion will double the passenger capacity of the airport and is needed to meet the demands of business travelers and visitors in and out of southwest Montana. The three story terminal building features exposed Glulam construction and serves as the lodge-themed center piece for the airport.

Western Wood Structures supplied the Glued Laminated members and Simpson hangers to the General Contractor, Martel Construction of Bozeman. The job required 18 pages of shop drawings to detail and schedule the nearly 2,000 individual laminated beams, purlins, columns, and trim pieces. The Glulams were manufactured by QB Corp. of Salmon, Idaho and the difficult fabrication was performed in the plant.

Educational Seminars

2011-02-24T10:53:00.000-08:00

Western Wood Structures is presenting two educational seminars next week to structural engineering groups.

The first seminar will be presented to the Structural Engineers Association of Maine on Monday February 28th starting at 5 pm. It will be held in the conference center of the Holiday Inn on Riverside Street in Portland, Maine.

The second seminar will be presented the following night to the Structural Engineers Association of Rhode Island. It will be held at the offices of Odeh Engineers, Inc. in North Providence, R.I. starting at 4:45 in the afternoon.

Paul Gilham, Chief Engineer for WWS, will be the speaker. The seminars will focus on the Rehabilitation and will highlight common problems that existing timber beams and trusses can have as well as what solutions are available to building owners for any required repairs and code upgrades. Case study examples will be used to illustrate the processes used by WWS for analyzing older structures as well as for the implementing of repairs.

The NAU Sky Dome

2011-01-20T10:05:00.000-08:00

During the late 1960’s, a citizen’s group in Flagstaff, Arizona suggested that a major activity center be built in town with the major consideration that it be large enough to accommodate Northern Arizona University athletic events. Nothing came of this recommendation but NAU President Dr. Lawrence Walkup did not give up on the idea.

Dr. Walkup followed through by conducting a study and polling the students who expressed a desire for a covered multi-purpose facility on the Northern Arizona campus. The students wanted an on-campus facility that would include a skating rink plus room for athletic events and entertainment programs. Dr. Walkup then developed a plan to build a covered multi-purpose complex for multiple uses. He began by consulting Architectural firms and asked for proposals.

The Architectural firm of Rossman & Partners of Phoenix was selected to design the facility and they presented the idea of a glued laminated timber dome that would cover 6 acres under one roof. Most of the funding for this project was provided by the Arizona State legislature and after plans were completed the University accepted the $6.6 million base bid from Mardian Construction Co. in August of 1975. Western Wood Structures acted as a sub-contractor to Mardian for design and construction of the VARAX style timber dome.

The 502’ diameter facility was very economical even by 1975 standards because of its unique style of construction. A natural bowl at the site was further excavated to allow for the domed roof to rest on 36 concrete buttresses at ground level. This “Ensphere” design eliminated the need for expensive outside support walls. As a result, athletic events as well as most of the spectator seating takes place 30 feet below ground level. There are 15,200 permanent seats but capacity can be increased to 20,000 with temporary end zone seating. The timber roof is designed to support the huge volumes of snow that accumulate in Flagstaff.

When it was completed, the 502’ diameter NAU Sky Dome was the largest clear-span timber roof in the world. Since then, Western Wood Structures has constructed two larger domes – the 530’ diameter Tacoma Dome and the 532’ Superior Dome on the Northern Michigan University campus.

The Cathedral of Christ The Light

2010-12-21T14:10:00.000-08:00

When the Cathedral of Francis de Sakes was rendered unusable following the 1989 Loma Prieta earthquake, the Archdiocese wanted to build a new Cathedral with a 300 year design life span. Glulam was selected as the main structural building component for its strength, durability, and aesthetic appeal.

The roof is composed of a large steel compression ring and a glass oculus. The oculus is supported by glass enclosed Glulam space frames consisting of 10-3/4” x 15” Glulam mullions that measure 103’ in length, 10-3/4” curved Glulam ribs that vary in depth from 30” to 19-1/2” and measure 97’ in length, and pre-tensioned steel rods that were manufactured in Germany.

Lathe turned Glulam compression struts connect the outer mullions to the interior ribs. Glulam louvers that vary in depth from 22-1/2” to 39” are set between each rib at seven different angles to optimize light effects.

Special attention was given to the appearance of the Glulam products. Lumber was hand selected by the manufacturers to minimize knots and voids on the exposed surfaces. Any voids were then left natural since standard fillers used to bring Glulam to Premium Appearance is often objectionable.

Western Wood prepared 67 pages of shop details from a three dimensional computer model to fully describe the Glulam components. In total, there are 26 vertical mullions, 26 curved ribs, 720 louvers, and 88 compression struts. The frames are connected with 249 unique steel assemblies and 42 unique rod assemblies.

Each Glulam member was pre-fabricated off site and many of the steel connector assemblies were plant installed to reduce jobsite costs. There were nearly 15,000 holes to pre-drill, all of which had to be accurately located. A hundegger machine was used to fabricate the louvers while the struts, ribs, and mullions were fabricated by hand. The long, curved ribs were trucked to the site from Minnesota and the rest of the Glulams were manufactured and fabricated in Oregon.

The jobsite’s proximity to busy downtown Oakland contributed to the construction challenges faced by Western Wood crews but assembly and erection of the Glulam system was achieved in just 3 months.

Wood Design & Building article.

Glulam Specifications

2010-11-17T13:40:00.001-08:00

Specifications for Glued-Laminated Timber or “Glulams” are usually found in Division 06180 of the CSI numbering format. Specifications are written by the specifier in order to establish the standards by which the supplier or installer of the product is expected to adhere. We are providing a sample specification for those who wish to keep current as many things have changed over the years. By clicking on the link below you will be able to view and copy this sample specification.

The Ford Foundation Building

Roseburg, Oregon

Specifications of Glued-Laminated Timber Sample

Lower Burnett Road Bridge

2010-10-25T10:24:00.000-07:00

The Foothills Rails-to Trails coalition of Buckley, Washington working in conjunction with Pierce County, had been seeking a link to connect the north and south sides of the Foothills Trail to replace the original railroad trestle that had been removed some years prior. The result is this stunning Arched Bridge that Western Wood Structures designed, fabricated, and installed.

The use of 3D modeling made possible for the bridge components to be fully fabricated prior to pressure treatment which in turn allowed Western Wood crews to complete the complex installation in less than two months. The overall length of the 3-span bridge is nearly 400 feet including approach spans and when complete the trail will measure more than 28 miles in length.

The use of pressure treated Douglas Fir Glulam as a bridge material perfectly complements the natural beauty of the wooded site.

STRUCTURE Magazine, October 2010 article

Dominion Creek Trestle

2010-09-29T09:40:00.000-07:00

This 100 year old former Milwaukee Railroad trestle that once carried freight trains through the Montana backcountry is being retrofitted as part of a Rails to Trails project to accommodate bicycles, ATVs, and snowmobiles. This project was made possible thanks to $850,000 in Federal stimulus funding and will open miles of the Milwaukee Road passage through the dense forest toward St. Regis, Montana.

Western Wood Structures supplied the pressure treated 6.75” thick Glulam deck panels which were segmented to match the curve of the trestle. The walkway, which measures about 650 feet and rests 100-feet above Dominion Creek, is 12’ wide with 3-foot pedestrian walkways on either side. The project will be 80% complete before the snow flies this year with final completion scheduled for next spring.

The General Contractor is Dick Anderson Construction of Great Falls, Montana. Western Wood Structures met the tight shipping schedule by having the pressure treated Douglas Fir Glulams delivered in 8 to 9 weeks.

Nisqually River Estuary Boardwalk

2010-08-23T15:09:00.000-07:00

Federal stimulus money was used to finance construction of the Nisqually River estuary boardwalk at the Nisqually River National Wildlife Refuge. The mile-long boardwalk is nearly half done and when complete it will be used to provide access out into the world of mudflats and tidal sloughs teeming with marine life and birds.

The project has reclaimed about 762 acres of the refuge, turning the delta back into the estuary and saltwater marsh it was before it was diked 100 years ago to create farmland. The goal is to restore habitat for salmon, shorebirds, and other creatures that thrive in estuaries.

The boardwalk superstructure is constructed from pressure treated Douglas fir. The preservative is ammoniacal copper zinc, or ACZA, which is approved for use by the U.S. Environmental Protection Agency. The decking is Port Orford Cedar Glulam. The boardwalk will have a life expectancy of 50 to 75 years. The U.S. Fish & Wildlife Service considered re-cycled materials for construction of this boardwalk but wood was chosen for its durability and strength.

Western Wood Structures designed this timber boardwalk and is in the midst of fabricating and shipping materials as of this writing. The General Contractor is Five Rivers Construction of Longview, Washington.

Award Winning Bridges

2010-06-30T10:51:00.000-07:00

Western Wood Structures has been designing and selling treated timber bridges for 40 years. We have been fortunate enough to have been involved in some very interesting projects and our bridge sales have led us to nearly every state in the union plus Japan, Taiwan, and China. We are proud to show off some of our award winning bridges.

Award Winning Timber Bridges

The Anaheim Ice Arena

2010-05-26T09:11:00.001-07:00

Engineered wood was chosen by Architect Frank Gehry for construction of the Anaheim Ice Arena for two reasons: budget and aesthetics. According to the Matt Construction, General Contractor, structural steel had originally been selected as the primary structural building product but the owner’s budget could not be met with steel. So after consulting with Western Wood Structures the switch to Glulam took place and the result was an affordable building that is aesthetically pleasing.

Eleven rows of large double-curved Glulam beams spaced at 24’ centers span two ice rinks in a saddle-shape. The main Glulams follow the curved shape of the exterior building profile and from the outside the curvature of the roof system resembles “mouse ears” a look that the owner, Disney Development, was seeking.

Moment splices were utilized to facilitate shipment of the curved Southern Yellow Pine Glulams from Albert Lea, Minnesota to downtown Anaheim.

The purlins are solid sawn Douglas fir timbers spaced at 48” centers and the roof sheathing is 1-1/8” T & G plywood. Installing the thick plywood to the 75-foot radius of the roof structure was not an easy task. The end walls are constructed of Glulam columns, sawn timber horizontal girts, and ½” fire retardant treated plywood. The arena meets the city fire codes because it is designed as Heavy Timber construction.

The dual rink facility has an NHL sized ice rink to meet the practice needs of the Anaheim Mighty Ducks and an Olympic sized rink to meet the community recreational skating needs as well as youth hockey leagues. Western Wood Structures installed this 88,000 s/f roof system in just 3 months.

Anaheim Ice Rink Case Study

Portland Bulk Terminals

2010-04-27T10:27:00.001-07:00

Western Wood Structures was awarded a contract in 1995 to design and construct a Heavy Timber building on the banks of the Willamette River at Terminal 5 on property owned by the Port of Portland. The clear-span building measured 160’ x 1475’ and is used to store potash, a salt-like fertilizer that is mined in Eastern Canada, railed to Portland, and stored until ready for export across the Pacific.

Potash is highly corrosive to metal which makes engineered wood the perfect choice of building components. The steel connections used in this building required a special three-step epoxy coating to protect it from exposure to the potash. A metal building for an application such as this would have been cost prohibitive.

Glulam Arches are spaced typically at 32’ centers to carry the main roof loads. Glulam purlins are spaced at 4’ centers between the Arches and the roof is sheathed with 1-1/8” T & G plywood. All city fire codes were satisfied due to the Type IV Heavy Timber design employed.

Each Arch was pinned at the concrete abutments and at the top as well. This allowed for much of the roof framing to be accomplished on the ground making erection much easier as the frames were lifted and pinned in pairs.

One end wall was panelized in sections in anticipation of future expansion. It was planned that this wall would some day be dismantled and re-used when the building was added on to.

In 2006 Western Wood was awarded the contract to design and construct the anticipated addition. This addition increased the length of the existing structure by 608’ resulting in a building that now measures 160’ x 2155’. The building is now the equivalent of six football fields in length. The floor area is now 344,800 s/f and to our knowledge this building is now the largest wood framed clear-span building in Oregon. By comparison, the Tillamook Air Museum which was originally built as a blimp hangar in the 1940’s, measures 296’ x 1072’ and has a floor area of 317,312 s/f. The Chiles Center dome at the University of Portland, also a WWS project, is the largest clear-span timber building in Oregon that we know of with a diameter of 305’.

Portland Bulk Terminal Case Study

Alaska Airlines Hangar

2010-03-22T10:32:00.000-07:00

Western Wood Structures received an inquiry from the Facilities Project Manager of Alaska Airlines in January of 2006. He contacted us because the Bowstring Trusses in their Anchorage aircraft hangar were failing. These trusses had been evaluated and “repaired” less than three years earlier and as it was presented to us “the previous structural improvements were apparently insufficient to prevent additional failures.”

The first step in meeting the needs of this client was to make a site inspection to evaluate the condition of the trusses and to map out their configuration as the original drawings were not available. Based on this initial inspection, we recommended shoring of the entire roof system be installed immediately. We then completed a structural analysis which enabled us to make the required repair recommendations and our proposal to perform these repairs was accepted.

The original hangar was built in 1954 and the hangar was added on to several years later. As a result, there were two types of Bowstring Trusses in this building – Arch Teco Trusses that were constructed from solid sawn lumber in a multiple leaf system and Tim Trusses which were constructed from Glulam. The repairs were extensive and included the following:

• All of the lower chords in the Arch Teco type trusses were replaced. The lower chords of all trusses were post tensioned using ½’ high strength cable to reduce the tension stresses in the wood members.
• All webs that exceeded an L/d ratio of 50 were stiffened by adding new structural members with screws and epoxy.
• The top chords of all trusses were strengthened by adding structural members to the sides with lag screws and epoxy.
• All web to top & bottom chord connections were strengthened using structural steel shapes.
• T-Struts were added to the lower chords of all trusses because the post tensioning cables placed the lower chords in compression.

From experience we know that Bowstring Trusses of these types have been affected by a series of changes that have rendered many of them as “dangerous members” as defined by International Existing Building Code which is further explained here. The factors described in this article contributed to the problems in this building but issues which were specific to this project added further. For instance, over framing was added which increased the dead load significantly. In addition, a drifting condition was introduced to the structure when new bay doors were added to the ends of the building. Finally, the snow load in Anchorage had been increased by code from 40 psf to 70 psf since the original building had been built.

Now that the repairs are completed, the trusses are in better condition than they day they were built and Alaska Airlines can count on the use of their hangar for many years.

Western Wood Structures was sought out for this project because of our expertise in this type of work and because we carry both an engineer’s license in Alaska as well as a contractor’s license. And it’s always rewarding to receive a nice letter from a client following the completion of a project.

The Cosumnes River Bridge

2010-02-25T10:59:00.000-08:00

Welcome to “Working Wonders With Wood”. My goal with this is twofold: 1) to utilize this space to spotlight recent projects that Western Wood Structures has been involved in, and 2) to make an attempt to keep people abreast of recent developments and changes in our industry.

Western Wood Structures is a sales and engineering company founded in 1969. Our product lines include timber bridges, heavy timber trusses, Arches, Glulam beams, and laminated decking with our primary focus on the commercial market. Many of the projects we sell are designed in house. We also fabricate some of the projects we sell in our shop as well as install some of them with our own field crews. Sometimes we act as a material supplier and sometimes as a sub-contractor depending on factors such as project location, current work load, and customer needs. It is not uncommon for a project to start out as conceptual and pass through every department here from sales to engineering to fabrication shop to our guys in the field after it becomes an order.

Western Wood Structures offers inspection services of existing timber buildings, primarily roof systems. We are often hired to make a site inspection, run an analysis, determine the cause of any problem, and make remedial recommendations. We can then design and implement structural repairs and code upgrades to timber beams and trusses which usually involve post tensioning, shear dowel reinforcement, or other strengthening methods. There will be more on this subject another time.

This first monthly entry will focus on one of our many outstanding timber bridges: The Cosumnes River Pedestrian Bridge outside of Rancho Murieta, California. This bridge measures 410’ in length with a center span of 200’ and side spans of 105’. It is 12’ wide and was constructed primarily for pedestrian traffic, golf carts, and bicycles but it is also designed to carry a 10,000 lb. maintenance vehicle. It was required by conditional use permit when property in the Rancho Murieta South housing development near Sacramento was developed for residential use.

Western Wood Structures worked under a General Contractor, Viking Construction of Rancho Cordova, CA. Quincy Engineers of Sacramento was responsible for the civil work as well as the design of the concrete abutments.

The main carrying members are Glulam Trusses. The main span features bowstring trusses while the outer spans are parallel chords. The top chords feature a reverse continuous curve to form a flowing appearance. The curved shape of the bridge was proposed by WWS to provide a deep section in the main span as well as a smooth transition to the outside spans. The reverse in curvature begins in the side span and the point of reversal takes place in the first top chord splice in the main span. A continual graceful curve from end to end was achieved and of course splices were introduced to allow for shipment and pressure treating. The curvature gives this massive bridge a sleek appearance. Glulam floor beams support the 2-1/2” thick Glulam deck panels to form the deck and the floor beams are located at panel points so the trusses are not point loaded.

The analysis determined the radii of the truss top chords and this information was transferred to our fabrication shop where they trusses were laid out, fabricated, and match-marked. All holes were drilled in the Glulam prior to pressure treating using the steel as templates which allows for a proper treating envelope around the entire member. This extra step will help to protect the member from insect or fungal attack. Western Wood Structures believes that a treated timber bridge will easily have a life span of 75 years if it is pressure treated, fabricated before treatment, and properly maintained.

Western Wood Structures crews assembled each truss on site including much of the deck prior to erection. Viking Construction was able to build a crane pad near the river to allow the crane to set up near the main span thus minimizing the reach of the main span which weighed almost 130,000 lbs. representing the heaviest lift Western Wood Structures has ever made. Each side span was just under half this weight. Jobsite assembly and erection took a 5 person crew six weeks to complete.

This magnificent treated timber bridge is not only functional and affordable but was also able to achieve all of the aesthetic requirements of the project. It provides the access needed for the residents while allowing greater utilization and appreciation of the community’s waterway.

We are very proud of the awards this bridge has won since its completion. It earned a Merit Award of Engineering Excellence from the Consulting Engineers and Land Surveyors of California [CELSOC] in 2008. And just last month it earned a Timber Bridge Design award from the California Region of Woodworks in the non-residential category.

I hope that you will check back monthly. We welcome your questions and comments.