There are currently numerous methods available to increase the stability of earthen embankments or to construct retaining walls. Retaining walls are generally constructed by excavating soil or rock at the desired location. Once the soil mass is excavated, the remaining soil mass is typically stabilized to prevent movement of that mass. Slope stability can be increased using soil nails. For example, a slope can be stabilized by drilling holes into an existing embankment, placing steel rods in those holes and then filling the holes with cementatious grouts. By concurrently placing the steel rods and cement into an existing embankment, the slope stability can be improved so that excavation can be completed in front of that stabilized embankment (i.e. in the plane perpendicular to the orientation of rods placed into the embankment), without risk of the embankment collapsing on the construction site. In another example, rods can also be placed into generally horizontally oriented shafts drilled into existing embankments. Following insertion of the rods into the shafts, concrete or high strength grout is injected into the shafts. The concrete or grout bonds the rods to the shaft, which results in a reinforced structural column within the soil mass of the embankment. There are currently many products that can be used to construct such ground anchored and or soil nailed structures.
Anchored structures can also be used to increase soil stability in situ. Anchored structures are tensioned or loaded so that the load is placed on the face of the in situ soil mass. This face load, which is induced by anchor tensioning, holds the face of the anchors and the in situ material at a predetermined position. In contrast, soil nails are typically not loaded or tensioned when they are installed, but become loaded as the earth in front of the soil nailed structure is removed. A minor amount of movement of a soil nail in situ embankment is typically assumed in design. Movement of the embankment is a manifestation of the stabilizing effect of the soil nails replacing the buttressing effect of the existing in situ material in front of the soil nailed structure.
Soil nails and anchors are prone to corrosion failures. For example, if the steel rods or steel strands are used as nails or anchors, they can corrode through contact with moisture and the soil. To minimize the effects of corrosion, products have been developed to protect metal rods or strands from corrosion. For example, the “Double Corrosion System” offered by the Dywidag-Systems International uses PVC pre-grouted sheathing over metal rods to provide a water tight barrier. Florida Wire and Cable, Inc., offers plastic sheaths over a flexible steel strand for use along soil anchors. Dywidag-Systems International also offers a “Dywidur” bar, which is a non-deformed fiberglass bar bolt. Such a bolt is suitable for use in highly corrosive soil, because it is resistant to corrosion. This bolt does not have significant deformation, so its use is limited in standard grout injection to providing a better bond to the drilled shaft. These products can be effective if installed properly and can offer extended life for the anchored structure.
For anchored structures, corrosion protection is a major consideration. Because metal bars used in such structures are anchored, they are more prone to break under that tension. Therefore, metal bars used in such applications typically have double or triple corrosion requirements to ensure against failure of the anchored slope. Additional corrosion protection adds to the cost of currently available soil reinforcement for anchored slope stability projects.
These and other corrosion-resistant products require proper installation to prevent damage to the corrosion-resistant coating material. The sites for such installations are generally uneven (e.g., mountainous or hilly), which requires heavy equipment. Such installation conditions increase the likelihood that damage might occur to the corrosion-resistant coating material. Because corrosion reduces the service length and load capacity of metal rods or cables, corrosion is a significant problem which limits the useful life of soil nailed or anchored structures.
Another typical application where ground anchors, tie backs or soil nail earth retention structures are used is for the support of temporary site excavations for construction of buildings and other structures. For some locations, such as urban areas, it can be desirable to have the ability to remove or cut through the stabilized earthen wall utilizing tie back ground anchors or soil nails. Future utility placement or maintenance in the streets or other right-of-way areas behind the shoring may necessitate either the removal of or the cutting of trenches through the in situ reinforcement used as shoring. Currently the use of steel materials dominates the types of shoring used. Due to the high shear strength of steel tendons, steel rods, or steel threadbars cutting through the material is both costly and time consuming, resulting in expensive improvements in right-of-way areas behind excavation sites shoring.
In view of these shortcomings of currently available devices for soil nailed or anchored structures, there is a need for soil nails and anchors that provide strength comparable to existing materials while providing improved resistance to corrosion and can be removed or cut if necessary.
The present invention provides methods that facilitate the construction of precast concrete post tensioned retaining walls. Both cast in place and precast concrete structures may utilize post-tensioning threadbars or SDB's with threadbar ends (as described in U.S. provisional patent application No. 60/261,486, Doc. No. 7291 filed Jan. 13, 2001, a continuation-in-part of PCT patent application number PCT/US01/05733, filed Feb. 22, 2001, which designates the United States of America and claims the benefit of U.S. provisional patent application No. 60/184,049, filed Feb. 22, 2000. Additionally described in U.S. patent application Ser. No. 10/047,080 filed on Jan. 14, 2002 which claims the benefit of U.S. patent application Ser. No. 10/342,758 filed on Jan. 14, 2003. This application claims the benefit of U.S. patent application Ser. No. 10/758,601 filed on Jan. 14, 2004.) to join and subsequently post-tension concrete components together. A typical method in current use is to provide a fixed tensioning anchor plate and nut assembly cast into the fixed concrete component to receive the threadbar connecting the components. To connect the two components a threadbar is inserted into the plate/nut assembly through the other joining component and the components are post tensioned together. Skilled tradesmen familiar with concrete forming practices are a prerequisite for correct placement of the plate nut assembly to precise tolerances so that threadbars will line up with the mating components.
Therefore there is a need for a post tension plate/nut anchor assembly that can compensate for slight placement errors that can be moved to the correct anchor location within reasonable tolerances cast in either precast or cast in place concrete components. The current invention provides means and methods that allows for movements of threadbars within a post tension anchor assembly after it has been cast into either precast or cast in place concrete as required for proper alignment of the threadbars.
Precast concrete structural applications that can utilize a variable location post tensioning anchor plate nut assembly include, but are not limited to, retaining walls formed by post tensioning components together to form a structural element comprised of at least two precast elements. One specific type of precast concrete retaining wall structure is formed by post tensioning precast tee shaped elements together (as described in as described in U.S. provisional patent application No. 60/261,486, Doc. No. 7291 filed Jan. 13, 2001, a continuation-in-part of PCT patent application number PCT/US01/05733, filed Feb. 22, 2001, which designates the United States of America and claims the benefit of U.S. provisional patent application No. 60/184,049, filed Feb. 22, 2000. Additionally described in U.S. patent application Ser. No. 10/047,080 filed on Jan. 14, 2002 which claims the benefit of U.S. patent application Ser. No. 10/342,758 filed on Jan. 14, 2003. This application claims the benefit of U.S. patent application Ser. No. 10/758,601 filed on Jan. 14, 2004) or by post tensioning generally tee shaped precast concrete sections to a conventional cast in place concrete foundation. Heretofore when tee sections have been used for an earth support structure, the post-tensioned anchor plate/nut assemblies used were fixed and immobile. The vertical post tensioning threadbars inserted into these fixed locations had no location flexibility therefore very precise placement of the anchors in the component is required so that the threadbars would line up with fixed anchor locations in the adjoining component. Placement of the post tensioned anchor plate/nut assemblies therefore required skilled workmen setting rigid templates placed on the proper grid to achieve correct placement of the anchors in the concrete foundation. Should errors occur in the placement process, substantial retrofitting and possibly a re-pour of a portion of a foundation would be necessary. Erroneous field situations then would both delay and add costs to the structure. The present invention allows for compensation of anchor placement errors, thereby eliminating or minimizing problems associated with misplaced post-tensioned anchor plate/nut assemblies. The following options described for the use of the present invention shown and described herein are for precast concrete earth retention structures wherein generally tee shaped sections that are vertically disposed for the retaining wall backfill support.
One configuration that can utilize the present invention is an earth retention structure utilizing tee sections that are generally vertically disposed and are post tensioned to a cast in place concrete foundation. The tee sections have a front face or flange section as well as “stems” that protrude form the back of the face. There can be only one tee stem or a single tee or multiple stem sections protruding from the back or flange of the generally tee shaped section. When in place for an earth retaining structure the protruding stem or stems will be in contact with and covered with the retaining wall backfill earthen material. Therefore the earth loads due to the wall fill will be transferred to the generally vertically disposed tee section. The tee sections used for this type of application are large sections that would typically be used for long span bridges and the like and would be generally horizontally disposed for these types of structures. When used for bridges these tee sections can span large distances well over eighty feet supporting vehicular bridge traffic. For the retaining wall applications described herein the retaining wall heights could be over fifty feet. To compensate for these tremendous earth loads the tees need to have an adequate section i.e. the protruding stems need to protrude a substantial distance for the face or flange of the tee into the wall fill. This distance or depth of the tee stem can be in the order of three to five feet as measured form the rear face of the tee section. Correspondingly the post tension threadbars that are placed in ducts in the rear portion of the stems need to be high strength capable of sustaining high tensile loads that could approach 500,000 pounds of tension in each stem. Therefore accurate placement of the post tensioning anchors for structures like these is critical since any mis-alignment could result in excessive localized stresses at the component interface connection.
Another application where the present invention can also be utilized is for vertical post tensioned tee section supports with panels spanning between tees for earth retention structures. When a cast in place foundation is used instead of a precast tee foundation, the vertical tees are post tensioned to a cast in place foundation. The tee sections are typically oriented in a generally vertically disposed orientation and each tee section is horizontally displaced from adjacent tee sections. The displaced distance closely corresponds to the lengths of the panel or panels supported by and bearing on the adjacent tee flanges. As with the previously described configurations, the variable position post tensioned anchor plate/nut assemblies can be cast into the foundation at locations that closely correspond to the post tension duct locations within the stems of the tee sections. Although standard, fixed, non-adjustable post-tension anchors could be used for the tee/panel combination without affecting the function of this earth retention configuration, placement of the fixed post-tensioned anchors is critical and must fall within close tolerances to avoid costly modifications. The anchors described in the present invention, placed in correspondence to the corresponding locations of the post-tension ducts within the stems of the vertically disposed tees, allow for movement of the post tension threadbars within the variable position post-tensioned anchor assembly. Since the anchor plate/nut assembly can be horizontally repositioned following the curing of the concrete foundation, minor placement errors can be compensated for with the use of the present invention. Therefore there is a need for an improvement in the existing technology relating to fixed post-tensioned anchor assemblies. The use of the present invention offers the advantage of future adjustment of the position of the anchor plate/nut assembly following installation of the anchors encapsulated and immobile in concrete thereby eliminating or minimizing subsequent structure modifications should placement tolerances be exceeded by improper field positioning of currently available conventional post-tensioning anchors.
These are but two examples of the use of a variable or adjustable location post-tensioned anchor plate/nut assemblies. The retaining wall assemblies utilizing the present invention are described in the following detailed descriptions.
It will be obvious to those familiar with post tensioning applications and skilled in the art that many other precast or cast in place concrete structural applications can benefit from the use of the present invention.
A partially constructed post-tensioned adjacent double tee earth retaining wall assembly 830 is depicted in the isometric sketch in
Referring now to
View “b” in
Enlarged views of the variable location base post tension anchors 850 are shown in views “c” and “d” in
A deviation from the plan location of a post tension threadbar 832 is shown in view “d” in
Two vertical section views of a variable position base post tension anchor assembly 850 and a typical fixed location post tension anchor assembly 870 in current use are shown in
Referring to view “b” in
Referring now to view “a” in
Referring now to
Horizontal sections (as indicated by the dashed cut section line in view “a”) through the post tension threadbar 832 are shown in views “b” and “c” in
In view “b” the post tension threadbar 832 has been rotated and threaded into the post tension nut 863 resulting in the rotation of the variable location stress plate washer 856 which is shown in contact with the void oversized enclosure duct 872 at the impingement point 859. As a result the variable location stress plate washer 856 is restricted from rotational movement allowing the post tension threadbar 832 to be threaded into the post tension nut 863 a sufficient distance for full thread contact prior to post tensioning. Following the insertion of the post tension threadbar 832 into the variable location stress plate washer 856 the post tension threadbar 832 can be both partially rotated or displaced horizontally within the confines of the threadbar void 866 as may be required to reasonably position the post tension threadbar 832 to the correct position. Although the post tension threadbar 832 can be displaced horizontally as needed for alignment the post tension threadbar 832 it is restricted from any vertical movement due to void stressing plate 854 which is necessary so that the post tension threadbar 830 can withstand vertical post tensioning loads.
Referring back again to view “a” in
A vertical cross section of a tee/footing wall assembly 860 is shown in
An isometric view of a partially constructed post tensioned tee/panel wall assembly 820 is depicted in
A partial plan view of a partially constructed post tensioned tee/panel wall assembly 820 is shown in
This application claims the benefit of U.S. provisional patent application No. 60/261,486, Doc. No. 7291 filed Jan. 13, 2001, and is a continuation-in-part of PCT patent application number PCT/US01/05733, filed Feb. 22, 2001, which designates the United States of America and claims the benefit of U.S. provisional patent application No. 60/184,049, filed Feb. 22, 2000. This application also claims the benefit of U.S. patent application Ser. No. 10/047,080 filed on Jan. 14, 2002. This application additionally claims the benefit of U.S. patent application Ser. No. 10/342,758 filed on Jan. 14, 2003. This application claims the benefit of U.S. patent application Ser. No. 10/758,601 filed on Jan. 14, 2004. This application also claims the benefit of U.S. patent application Ser. No. 11/300,055 filed on Dec. 14, 2005. These patent applications are incorporated by reference herein in their entirety.
Number | Date | Country | |
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Parent | 10758601 | Jan 2004 | US |
Child | 11330758 | US |