SIMPLIFIED DESIGN METHODS OF 



TREATED ,TIMBER STRUCTURES 



FOR 



SHORE, BEACH, AND IvlARINA CONSTRUCTION 



by 



James Ayers and Ralph Stokes 



I. INTRODUCTION 



Pressure-treated timber has wide application in the waterfront and 

 shore protection structures that are built in marina developments and 

 other shore and beach locations bordering on bays, lakes, and river 

 resorts. Because of its strength, durability, and economy, pressure- 

 treated timber is the principal construction material for bulkheads, 

 seawalls, piers, and groins at locations with mild exposure and shallow- 

 to -intermediate water depths. 



II. TIMBER BULKHEADS 



Bulkheads are boundary structures that separate land from water 

 (Figures 1, 2, and 3). They are built along shorelines and waterways 

 and on the periphery of harbor developments, serving to retain earth 

 usually by means of a vertical wall. The wall is made of timber sheet 

 piles driven into the ground for support against outward movement. The 

 tops of the sheet piles bear against a horizontal distributing member, 

 or wale, connected to an anchor system by steel tie rods. 



Tliere are two general types of anchor systems. The passive- 

 resistance type (Figures 1 and 2) uses buried timbers located well below 

 the finished ground surface at some distance behind the sheet piles. 

 Earth pressure prevents displacement of this type of anchorage. The A- 

 frame anchor (Figure 2) derives its resistance from the structural 

 action of round timber piles arranged in groups. Some piles are verti- 

 cal; others are battered (inclined). Suitable connections between piles 

 enable the A-frame to resist lateral displacement by developing thrust 

 in the batter piles and uplift in the vertical piles. Although either 

 type of anchorage system may be used alone or in combination for any 

 type of bulkhead, the A-frame is generally used for the higher bulk- 

 heads because it develops a greater resistance to the pull of the tie 

 rod. 



Seawalls are protective retaining structures that occupy an advanced 

 position along a shoreline as barriers to wave attack. Seawalls are not 

 clearly distinguishable from bulkheads. A vertical-faced retaining 

 structure that is subject to direct wave attack of some degree of inten- 

 sity is classified as a seawall, whereas a similar vertical-faced 

 structure alongside a relatively quiet harbor waterfront, with little 

 or very mild wave action, is classified as a bulkhead. 



