allaboutpai.com → Tha Pai Bridge

The following piece was researched and written by Hak Hakanson, who long ago worked as a bridge inspector for the US State of Pennsylvania and clearly remains dedicated to the subject! This page is part of allaboutpai.com, which has lots of information about Pai, a town in the mountains of Northern Thailand.

The Mystery of Tha Pai Bridge

By Hak Hakanson

For the last several decades, Pai locals and tourists alike have visited the so-called "Japanese WWII Bridge," an old steel truss bridge that crosses the Pai River right alongside main highway 1095, about 4km south of Pai in the hot spring village of Tha Pai. However, as this document will reveal, the bridge is most definitely not of Japanese origin. In 2007, in order to elevate its status as a tourist attraction, the bridge was renovated and repainted, and a new and permanent public display was added at the southeast approach. The new display corrects the story somewhat, admitting that the steel truss bridge was erected not by the Imperial Japanese Army during WWII, but rather by a Thai government entity around 1976. However, the new display claims that the bridge spans come from the old Nawarat Bridge in Chiang Mai (which was removed around 1966 to make way for the current reinforced concrete structure). As this document will clearly show, this is also not the case!

So we have ourselves a mystery. Where did the spans of this bridge really come from? Were they added at the same time? Do verifiable photos exist of any bridge at this river crossing from WWII?

These are open questions for all the readers out there. In the sections below, we present the evidence available so far, and we invite any readers out there with further information, photos, or references to contact us at:

This page is an excerpt from a larger, detailed, evolving report about the Tha Pai bridge; email us at the address above if you're interested in seeing the full report.

Not the Nawarat

Any connection between the Tha Pai Bridge and the old Nawarat Bridge is easily disproven by a simple comparison of the two.

The appearance of the older bridge is well documented with photos hanging throughout Chiang Mai [photo by author of a print at Wat Gate Museum, originally taken by Boonserm Satrabhaya]:

Nawarat Bridge

Another more detailed photo of the old Nawarat Bridge [photo by author of a print at Wat Gate Museum; source is unknown]:

Nawarat Bridge

led to this schematic (not to scale) rendering of one span, which is a curved top chord Parker through-truss [schematic drawing by author; all truss names in this article are per Bridge Basics at http://pghbridges.com/basics.htm]:

Nawarat Bridge Span Schematic

The other four spans of the old Nawarat Bridge were identical.

In contrast, the old Tha Pai Bridge is made up of four different types of trusses, some configured as 'through-trusses', others as 'pony-trusses', plus one very simple span, Span S3. Schematically, the old bridge looks something like this, as viewed from the north:

Tha Pai Bridge Span Schematic

Counting from the east (the Chiang Mai end of the bridge, going in the same direction as highway stationing is increasing), the first two, identical spans (S1 & S2) of the old Tha Pai bridge are Warren trusses, modified with verticals, having straight and horizontal top chords [photo by author, 12 Jul 2008]:

Tha Pai Bridge Spans S1 and S2, with Span Schematic

Tha Pai's Warren trusses are quite different from the Parker trusses of the Nawarat. Should the question arise, no, it wouldn't have made economic sense to have modified two spans from the Nawarat to take on this new appearance.

Thus, spans S1 and S2 of the Tha Pai River Bridge could not have come from the old Nawarat Bridge.

Following the first two through-truss spans is a very short span, S3, made of simple beams—no trusses [photo by author; 11 Feb 2008]:

Tha Pai Bridge Span S3

It is an odd detail, but the point is that the steel for that span did not come from the Nawarat.

The next three spans, S4, S5, & S6, while not identical, are all pony trusses. The "outer" spans, S4 and S6, are similar in configuration, though different in length, and approximately symmetrical around an arched center span, S5. The truss configuration might best be classified as a Warren truss, modified with misplaced verticals. Top chords for S4 and S6 are straight and horizontal while that for S5 is curved [photo by author; 11 Feb 2008]:

Tha Pai Bridge Spans S4, S5, and S6

Tha Pai Bridge Spans S4, S5, and S6

The general symmetry of the three spans plus the same, unusual (indeed, peculiar) truss design suggests that they probably came from a single bridge of three spans. Further, in Span S4 is this "United States Steel Products Company 1930" manufacturer's tag—inconsistent with the Nawarat, which, according to a caption on a photo at Wat Gate Museum, was fabricated by "Cliffland Company, England" [photo by author; 09 Jan 2009]:

Tha Pai Bridge Manufacturer's Tag

It is safe to say that none of the Spans S4, S5, and S6 came from the old Nawarat.

The last span, S7, is a pony truss, of a military expeditionary type—a Bailey Bridge [photo by author; 11 Feb 2008]:

Tha Pai Bridge Span S7

The technology used in fabricating Span 7 is a generation later than that used in the old Nawarat Bridge. It could not have come from the Nawarat.

The simple conclusion to be drawn is that none of the spans on the old Tha Pai steel bridge came from the old steel truss Nawarat Bridge.

That said, the old Tha Pai Bridge, as it stands today, offers a unique selection of steel truss bridges in one spot that should be properly identified, described, and evaluated, for all to enjoy.

In that vein, many, many questions need to be answered, such as:

• Do verifiable photos exist of the bridge at the river crossing from WWII?

• From where were the three main sets of spans (S1 & S2; S4, S5 & S6; S7) relocated?

• Does anyone know any details about those spans, such as manufacturer or date of manufacture?

• Is there any record of spans S1, S2 & S3 having been added at a date later than the other spans (this is one possible explanation for Piers P2 & P3 being so close together)?

• Why are the trusses in spans S4, S5 & S6 so peculiarly configured?

Again, we welcome any and all ideas, comments, or speculation at:

Copyright

Text and images from Hak's article are copyright 2009 Hak Hakanson.

Shameless Plugs

The following shameless plugs are from Chris Pirazzi, the creator of allaboutpai.com, not Hak Hakanson: