Monthly Archives: October 2012

Quite Laterally, Here We Go Again –

Frequent fliers likely recall my June entry Meritocracy, (click on the highlighted & underlined text to be linked to the entry) in which I puzzled over the frequency with which contracts to repair and rehabilitate wooden spans are often awarded to companies who, know the ins and outs of bidding public works projects, but who hold nothing in their scope of experience to suggest they have the required tooling, knowledge, or abilities, to in-house execute such work. And somehow, nor are they necessarily required to pre-qualify, or ride the resumé of pre-qualified specialist subcontractors when preparing proposals to bid such contracts. Recent turns of event have again shown how sadly and commonly this circumstance happens.

A recent string of extreme truck damage incidents, leaving horrific levels of Portal to Portal damage, have splintered Tie Beams or dislodged and distorted Tie Rods and ruptured Braces in Upper Lateral Bracing Systems, in two bridges, one in Pennsylvania, one in Indiana.

Though it is often overlooked, complexity in a bridges framing is not limited to the Trusses proper. In some Truss types such as Towns, the more demanding framing is that found in the connecting systems which unify the two trusses and complete the “Through Truss”.

Tie & Lateral Bracing systems are far from simple carpentry, but are a complex bit of advanced Timberframing. (for all the camber driven subtleties and varied reasons I articulated in Meritocracy – Foremost among these being that proper fit requires the acknowledgement that these shoulders and abutments are, more often than not, not “simple” angles, but are in point of fact, compound angles. These necessarily need be laid out and cut to match real world camber driven circumstance – To drive home this point > In Bridge work, every joint which fails to have hard up full bearing through not just the visible portions, but the entirety of the joint, means undue crush and loss of geometry – This including, loss of camber) This circumstance of navigational error truck damage taking out such systems near or in their entirety, and the developing response to it, does drive home particularly well, this paradox of contracting concrete and steel outfits to repair or rehabilitate wooden bridges. At least it does from my perspective – Maybe from yours.

From mine, the perspective is particularly sharp. I cut my Bridgewrighting teeth on Laterals. I came into my first bridge rehab with seasoned timber joinery chops, and was pointed at Laterals – I took it as the performance challenge it was…

Since then, Laterals have kinda been my thing, and I’ve been privileged to help replicate whole sets. Both, all too many Lowers lost to high water, and the flotsam it inevitably carries with it. And in an odd bit of happenstance, multiple sets of Uppers & Ties lost to wet heavy snowload driven roof collapse on three different bridges in three different States. These all lost decades before, (one the year before I was born) and either badly replicated, or done with an inappropriately heavy species, or both, or replaced with inappropriate, not true to original framing systems. I have also of course, helped replace Wind Braces, as well as Ties & Laterals lost to truck damage.

These Bracing systems tend to vary in detail, this sometimes driven by Truss Type, and sometimes by regional norms, the date of construction, or the preferences of the Bridgewright who built the span.

Repair / replacement of the truck damaged Pennsylvania spans upper timber-work was recently awarded to a highway construction outfit. It had / has the Wind Braced Ties and Over / Under Laterals typical to Town Trusses, the dominate Truss type in that corner of PA. It remains to be seen if they will subcontract in a concern with a familiarity in these materials and construction methods to replicate the destroyed framing.

Said to be the work of Nichols Powers, in this “Village Bridge” NH’s Ashuelot, (Ash-wool-it) the terminus for the Lateral Bracing load was formerly shared by two Ties through this Centered Straining Beam- The Design Engineer specified placement of a final set of Double Laterals in either end bay as part of a late 90’s restoration.

I’ve long admired this detail used on Indiana’s Williams – Often incorrectly attributed to JJ Daniels, The Williams is a product of the Massillon Bridge Co.

In process Scribe layout of a Lower Lateral to replacement Floor Beams at Maryland’s Gilpin’s Falls – For more information on this Floor and the now unusual Rebated Sleepers seen here – See the May of ’11 & June of ’13 Archives

The most recent truck damage repairs I’ve had a hand in mending – Portal to Portal damage to the 266′ Mt. Orne

Also Scribed in-situ – The normally unseen connection where the Mt. Orne’s Laterals join each other

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