Abstract:
Architectural precast concrete construction relies on mechanical connectors at discrete locations that may be damaged in a blast or seismic event, posing specific design problems to the engineer. These problems can be overcome with proper detailing. The performance of precast concrete cladding wall panel connection details may be enhanced by incorporating a specific connection hardware, herein described, that deforms elastically or inelastically to accommodate relative displacements due to building motion and/or energy associated with blast pressures.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/156,654, filed May 4, 2015, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Architectural precast panels are widely used in the commercial construction industry. They provide a low cost and efficient exterior paneling system for multistory buildings. Architectural panels also have the s chedule advantage of being fabricated off-site and then transported to the building site when needed. Architectural precast panels are easy to install and are relatively easy to repair when compared to other forms of exterior panel construction. 
     Architectural precast construction relies on mechanical connectors at discrete locations that are subjected to very large forces in a blast event, posing specific design problems to the engineer. These problems can be overcome with proper detailing. 
     Architectural panels typically have a row of connections at the top of the panel and row of connections at the bottom of the panel. Some architectural panels also have a row of connections along the sides of the panels. These connections are then attached to the structure through mounting brackets that are welded to the structural steel frame or embedded in the structural concrete. 
     For aesthetic reasons it is usually desired to have the panels as close together as possible. The gaps between the panels are typically filled with an elastomeric sealant Large gaps between panels are visually unattractive and the sealant must be maintained more frequently than the architectural panels. Multistory buildings are flexible structures that are designed to accommodate external forces. Common forces include horizontal and vertical ground forces (e.g earthquakes) or horizontal forces (e.g. wind pressure and blast pressure). 
     Although the internal steel structure is flexible, the exterior architectural panels are relatively rigid in comparison. When an external force causes the building to flex the panel connections must accommodate relative movements between flexing structure and the rigid panels. The capacity of a panel to deform significantly and absorb energy is dependent on the ability of its connections to maintain integrity throughout the blast response. If connections become unstable at large displacements, failure can occur. The overall resistance of the panel assembly will reduce, thereby increasing deflections or otherwise impairing panel performance. 
     It is also important that connections for blast loaded members have sufficient rotational capacity. A connection may have sufficient strength to resist the applied load; however, when significant deformation of the member occurs this capacity may be reduced due to buckling of stiffeners, flanges, or changes in nominal connection geometry, etc. 
     Both bolted and welded connections can perform well in a blast environment, if they can develop strength at least equal to that of the connected elements (or at least the weakest of the connected elements). 
     For a panel to absorb blast energy (and provide ductility) while being structurally efficient, it must develop its full plastic flexural capacity which assumes the development of a collapse mechanism. The failure mode should be yielding of the steel and not splitting, spilling or pulling out of the concrete. This requires that connections are designed for at least 20% in excess of the member&#39;s bending capacity. Also, the shear capacity of the connections should be at least 20% greater than the member&#39;s shear capacity, steel-to-steel connections should be designed such that the weld is never the weak link in the connection. Coordination with interior finishes needs to be considered due to the larger connection hardware required to resist the increased forces generated from the blast energy. 
     Where possible, connection details should provide for redundant load paths, since connections designed for blast may be stressed to near their ultimate capacity, the possibility of single connection failures must be considered. Consideration should be given to the number of components in the load path and the consequences of a failure of any one of them. The key concept in the development of these details is to trace the load or reaction through the connection. This is much more critical in blast design than in conventionally loaded structures. Connections to the structure should have as direct a load transmission path as practical, using as few connecting pieces as 
     Rebound forces (load reversal) can be quite high. These forces are a function of the mass and stiffness of the member as well as the ratio of blast load to peak resistance. A connection that provides adequate support during a positive phase load could allow a member to become dislodged during rebound. Therefore, connections should be checked for rebound loads. It is conservative to use the same load in rebound as for the inward pressure. More accurate values may be obtained through dynamic analysis and military handbooks. 
     The protection of multistory buildings to damage from earthquakes is described in the prior art. U.S. Pat. No. 3,638,377 issued on Dec. 3, 1969 to Caspe, describes an earthquake resistant multi-story structure that isolates the structure from the relative ground motions. U.S. Pat. No. 3,730,463 issued on Apr. 20, 1971 to Richard, describes a shock mounting apparatus to isolate the building footings. U.S. Pat. No. 4,166,344 issued on Mar. 31, 1977 to Ikonomen describes a system that allows the relative motion of a building structure relative to the ground using frangible links. 
     Architectural precast concrete can also be designed to mitigate the air pressure effects of a bomb blast. Rigid façades, such as precast concrete, provide needed strength to the building through in-plane shear strength and arching action. However, these potential sources of strength are not usually taken into consideration in conventional design as design requirements do not need those strength measures. Panels are designed for dynamic blast loading rather than the static loading that is more typical. Precast walls, being relatively thin flexural elements, should be designed for a ductile response. There are design tradeoffs between panel stiffness and the load on panel connections. For a surface blast, the most directly affected building elements are the façade and structural members on the lower four stories. Although the walls can be designed to protect the occupants, a very large vehicle bomb at small standoffs will likely breach any reasonably sized wall at the lower levels. There is also a decrease in pressure with height due to the increase in distance and angle of incidence of the air blast. Chunks of concrete dislodged by blast forces move at high speeds and are capable of causing injuries. 
     Therefore, what is desired is an improved system for connecting pre-cast architectural panels to the structure of the building to accommodate structural movements during earthquakes or high forces due to air pressure events. 
     SUMMARY 
     Architectural precast construction relies on mechanical connectors at discrete locations that may be damaged in a blast event, or large seismic event posing specific design problems to the engineer. These problems can be overcome with proper detailing. Precast concrete cladding wall panel connection details may be strengthened compared to conventional connections by incorporating a significant increase in connection hardware, the present inventive subject matter describes the connection details that improve the performance of architectural precast concrete cladding systems subjected to seismic and blast events. 
     In its broadest form, the inventive subject matter provides an embodiment describing a system for protecting the interiors of a building from earth quakes and explosive blasts, mainly comprising of precast architectural panel connectors. The precast architectural panel connector is comprised of a (i) precast panel mounted on to a building structure; (ii) a structural element, which is connected to the precast panel via a threaded rod and a bracket. (iii) crushing tube being placed on the threaded rod, which is positioned against the bracket by using adjusting nuts (iv) a coil spring placed on the threaded rod between the nuts and the crushing tube. 
     An embodiment of the present inventive subject matter describes an impact absorbing apparatus for a precast architectural panel connector comprising a crushing tube, the crushing tube having a hollow tube like structure with a rectangular cross section. A first face of the rectangular tube like structure having a central aperture and the second face being flat and also having a central aperture; further the first face being parallel to the second face of the rectangular tube frame like structure. The central aperture is adapted to receive a threaded rod which can bring in an impact such that upon impact, the first face of the crushing tube is resiliently deformed thus absorbing the impact, and the second face still remaining intact. 
     A further embodiment of the present inventive subject matter describes an impact absorbing apparatus comprising of a coil spring that is positioned on the threaded rod between the adjusting nut and the crushing tube or the structural bracket. The spring absorbs impact energy by elastic compression and returns to its original shape after impact. 
     A further embodiment of the inventive subject matter describes a method for installing an architectural panel connector comprising the steps of: (i) mounting a precast panel on to a building structure; (ii); (ii) connecting the precast panels to the structural elements via a threaded rod and a bracket; (iii) placing crushing tubes on both sides of the bracket; (iv) adjusting the position of the crushing tubes against the brackets by using the adjusting nuts (v) placing a coil spring on the threaded rod between the nuts and the crushing tube. 
     These and other embodiments are described in more detail in the following detailed descriptions and the FIG.s. The foregoing is not intended to be an exhaustive list of embodiments and features of the present inventive subject matter. Persons skilled in the art are capable of appreciating other embodiments and features from the following detailed description in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view assembly drawing. 
         FIG. 2  is a close-up view of the components surrounding a crushing tube and a coil spring. 
         FIG. 3  is a close-up view of the effect on the crushing tube when relative force of an architectural panel exceeds a predetermined amount in an inward direction. 
         FIGS. 4A and 4B  is a close-up view of the effect on the crushing tube when relative force of the architectural panel exceeds a predetermined amount in an outward direction. 
         FIGS. 5 and 5A  is a close-up view of the crushing tube. 
         FIG. 6  is an installed view of the crushing member. 
         FIG. 7  is a graphical representation of variation of load with respect to displacement for a 8″ inch crushing tube. 
         FIG. 8  is a graphical representation of variation of load with respect to displacement for a 8.5″ inch crushing tube. 
         FIG. 9  is a graphical representation of variation of load with respect to displacement for a 9.0″ inch crushing tube. 
         FIG. 10  is a graphical representation of the cumulative results of experimental results and theoretical predictions. 
     
    
    
     OVERVIEW OF THE SELECTED REFERENCE CHARACTERS 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Pre-cast panel 
                 110 
               
               
                   
                 Pre-cast panel width 
                 112 
               
               
                   
                 Pre-cast panel distance from  
                 114 
               
               
                   
                 pre-cast panel to structure  
                   
               
               
                   
                 Pre-cast panel to panel gap 
                 116 
               
               
                   
                 Building floor 
                 120 
               
               
                   
                 Perimeter Structural Beam 
                 130 
               
               
                   
                 Bracket 
                 140 
               
               
                   
                 Threaded Rod 
                 150 
               
               
                   
                 Adjusting Nut 
                 160 
               
               
                   
                 Bearing Connection 
                 170 
               
               
                   
                 Crushing Tube 
                 180 
               
               
                   
                 Coil Spring 
                 200 
               
               
                   
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION 
     The representative embodiments are shown in  FIGS. 1-6 , where similar features share common reference numerals. The notation ′ ″ or characters A,B,C etc represent a repetition of the same element. 
     Now referring to  FIG. 1  which illustrates a side view of a multistory building  100  with architectural pre-cast panel  110  mounted on the side of the building, typically mounted one per building floor  120 . The architectural pre-cast panel  110  is connected to the perimeter structural beam  130  using a bracket  140  via a threaded rod  150 . The threaded rod  150  is securely affixed to the architectural pre-cast panel  110 . At the base of the architectural pre-cast panel  110  is a bearing connection  170  that supports the weight of the architectural pre-cast panel  110 . The architectural pre-cast panel  110  is positioned relative to the building floor  120  by adjusting nuts  160 A/ 160 B that are threaded onto the threaded rod  150 . Placed on the threaded rod  150  are crushing tubes  180 A/ 180 B. The adjusting nut  160 A/ 160 B are tightened against the crushing tubes  180 A/ 180 B. 
     Now referring to  FIG. 2  which shows a close-up view of the crushing tubes  180 A/ 180 B which are placed on the threaded rod  150  on either side of the bracket  140 . The crushing tubes  180 A/ 180 B are tightened against the bracket  140  via the adjusting nut  160 A/ 160 B on either side of the crushing tubes  180 A/ 180 B. The coil spring  200  is placed on the rod between the crushing tube and the adjusting nut. 
     Now referring to  FIG. 3  which shows an inward lateral movement  148  of the bracket  140  that is attached to the structural beam  130  relative to the pre-cast panel  110 . The inward movement deforms  192 B the crushing tube  180 B and creates a deformed crushing tube  190 B. 
     Now referring to  FIG. 1 ,  FIG. 2  and  FIG. 4A , whereby  FIG. 4A  shows an outward lateral movement  144  of the bracket  140  that is attached to the structural beam  130  relative to the precast panel  110 . The outward movement compresses the coil spring  200  and creates a fully compressed spring  210 . 
     Now referring to  FIG. 1 ,  FIG. 2  and  FIG. 4B , whereby  FIG. 4B  shows an additional outward lateral movement  145  of the bracket  142  that is attached to the structural beam  130  relative to the pre-cast panel  110 . The additional outward movement deforms the crushing tube  180 A and creates a deformed crushing tube  190 A. 
     Now referring to  FIG. 5  which shows a close up view of the crushing tube  180 A and a side view of the crushing tube  180 B is as shown in  FIG. 5A . 
     Now referring to  FIG. 6  which depicts a representative assembly having the threaded rod  150  that is approximately one inch in diameter with nuts that can thread on the rod. The crushing tube may have dimension of four or six or eight inches in height and two or three inches in width. It should appreciated by those of ordinary skill that the specific dimensional descriptions are exemplary only. Crushing tubes with other dimensions may be used that generally fall within the spirit and scope of the present inventive subject matter. The threaded rod  150  is typically connected to the architecture panel via an embedded u-shaped bar that has a welded plate to allow the passage of the threaded rod. Other means of securing the rod to the panel could be devised without changing the concept of the system. 
       FIGS. 7, 8 and 9  are the graphical representation of the variation of yield load with respect to displacement for an 8 inches, 8.5 inches and 9.0 inches crushing tube respectively. 
     Table-1 given below shows variation of yield with load for an 8 inch crushing tube.  FIG. 7  describes the graphical representation  700  for the same. Thus for a 8 inches crushing tube the yield load increases with increasing displacement  710  and plateaus  720  at 10,750 pounds. 
     
       
         
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                   
                 8 inches 
               
             
          
           
               
                   
                 S.N 
                 Load 
                 PSI 
                 delta 
               
               
                   
                   
               
             
          
           
               
                   
                 1 
                 500 
                 100 
                 0 
               
               
                   
                 2 
                 1550 
                 500 
                 0 
               
               
                   
                 3 
                 2850 
                 1000 
                 1/32 
               
               
                   
                 4 
                 3550 
                 1250 
                 1/32 
               
               
                   
                 5 
                 4175 
                 1500 
                 3/64 
               
               
                   
                 6 
                 4850 
                 1750 
                 1/16 
               
               
                   
                 7 
                 5500 
                 2000 
                 1/16 
               
               
                   
                 8 
                 6800 
                 2500 
                 1/8  
               
               
                   
                 9 
                 8175 
                 3000 
                 5/32 
               
               
                   
                 10 
                 9450 
                 3500 
                 7/32 
               
               
                   
                 11 
                 10750 
                 4000 
                 1/4  
               
               
                   
                 12 
                 10750 
                 4000 
                 5/16 
               
               
                   
                 13 
                 10750 
                 4000 
                 3/8  
               
               
                   
                 14 
                 10750 
                 4000 
                 7/16 
               
               
                   
                 15 
                 11400 
                 4250 
                 1/2  
               
               
                   
                 16 
                 10750 
                 4000 
                 9/16 
               
               
                   
                 17 
                 10750 
                 4000 
                 11/16  
               
               
                   
                 18 
                 10750 
                 4000 
                 13/16  
               
               
                   
                 19 
                 10750 
                 4000 
                 7/8  
               
               
                   
                 20 
                 10750 
                 4000 
                 1 
               
               
                   
                 21 
                 10750 
                 4000 
                 1 1/8    
               
               
                   
                 22 
                 10750 
                 4000 
                 1 1/4    
               
               
                   
                   
               
             
          
         
       
     
     Table-2 given below shows variation of yield with load for an 8.5 inch crushing tube.  FIG. 8  describes the graphical representation  800  for the same. Thus for a 8.5 inches crushing tube the yield load increases  810  with increasing displacement and plateaus  820  at 11,400 pounds. 
     
       
         
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                   
                 8.5 inches 
               
             
          
           
               
                   
                 S.N 
                 Load  
                 PSI 
                 delta 
               
               
                   
                   
               
             
          
           
               
                   
                 1 
                 1550 
                 500 
                 0 
               
               
                   
                 2 
                 2850 
                 1000 
                 0 
               
               
                   
                 3 
                 4175  
                 1500 
                  1/32 
               
               
                   
                 4 
                 4850 
                 1750 
                  1/16 
               
               
                   
                 5 
                 5500 
                 2000 
                  1/16 
               
               
                   
                 6 
                 6800  
                 25000  
                  3/32 
               
               
                   
                 7 
                 8175  
                 3000 
                 1/8 
               
               
                   
                 8 
                 9450 
                 3500 
                  3/16 
               
               
                   
                 9 
                 10750 
                 4000 
                 1/4 
               
               
                   
                 10 
                 11400 
                 4250 
                  5/16 
               
               
                   
                 11 
                 11400 
                 4250 
                 3/8 
               
               
                   
                 12 
                 11400 
                 4250 
                 1/2 
               
               
                   
                 13 
                 11400 
                 4250 
                 5/8 
               
               
                   
                 14 
                 11400 
                 4100 
                 3/4 
               
               
                   
                 15 
                 11000 
                 4000 
                 15/16 
               
               
                   
                 16 
                 10750 
                 4000 
                 1 1/16  
               
               
                   
                 17 
                 10750 
                 4000 
                 1 3/16  
               
               
                   
                   
               
             
          
         
       
     
     Table-3 given below shows variation of yield with load for a 9.0 inch crushing tube.  FIG. 9  describes the graphical representation  900  for the same. Thus for a 9.0 inch crushing tube the yield load increases with increasing displacement and plateaus  920  at 12,800 pounds. 
     
       
         
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                   
                 9.0 inches 
               
             
          
           
               
                   
                 S.N 
                 Load 
                 PSI  
                 delta 
               
               
                   
                   
               
             
          
           
               
                   
                 1 
                 1550 
                 500 
                 0 
               
               
                   
                 2 
                 2850 
                 1000 
                 0 
               
               
                   
                 3 
                 4175 
                 1500 
                  1/32 
               
               
                   
                 4 
                 4850 
                 1750 
                  1/16 
               
               
                   
                 5 
                 4850 
                 2000 
                  1/16 
               
               
                   
                 6 
                 6800 
                 2500 
                  3/32 
               
               
                   
                 7 
                 8175 
                 3000 
                 1/8 
               
               
                   
                 8 
                 9450 
                 3500 
                  3/16 
               
               
                   
                 9 
                 10750 
                 4000 
                 1/4 
               
               
                   
                 10 
                 12050 
                 4500 
                  5/16 
               
               
                   
                 11 
                 12050 
                 4500 
                 3/8 
               
               
                   
                 12 
                 13400 
                 5000 
                 1/2 
               
               
                   
                 13 
                 14041 
                 5250 
                 5/8 
               
               
                   
                 14 
                 13400 
                 5000 
                 3/4 
               
               
                   
                 15 
                 13400 
                 5000 
                 15/16 
               
               
                   
                 16 
                 12700 
                 4750 
                 1 1/16  
               
               
                   
                 17 
                 12700 
                 4750 
                 1 3/16  
               
               
                   
                   
               
             
          
         
       
     
     The moment carrying capacity of a steel member M P  also called as the plastic moment for the section of the tube wall can be calculated by the formula M P =Fy (Yield Stress)*z (Plastic section modulus); M P =57,290*b*0.188 2 /4; M P =506*b: Where b=Tube Length 
     Further the yield load “P” on the whole tube can be calculated by the formula
 
 P* 0.62=4 M   P (1/2.625),thus  P= 2.46 M   P  
 
     By assuming a 10% over strength factor, P=1245.3*1.1*b=1370*b 
     For b (Tube Length)=4 inches: P=5480 Pounds 
     For b (Tube Length)=12 inches: P=16440 Pounds 
       FIG. 10  represents the graphical representation  1000  of the cumulative results based on the experimental findings and the theoretical predictions. Length of the tube (in inches) is plotted on the horizontal axis and the yield load (in pounds) is plotted on the vertical axis.  1010  and  1030  represent the two end points determined by theoretical calculations described above. The three central points  1020  are determined by experimental results described in  FIGS. 7, 8 and 9 . The linear equation for the line drawn through the experimental and theoretical results can be generally represented by y=1380.5x−83.796 with R 2 =0.9949. The conclusion drawn by these efforts is that the yield load is linearly proportional to tube length. This allows for designing the crushing tube to conform to the specific requirements of each application. 
     Referring to Table-4 which represents the mill certificate showing the results for manufactured product—ASTM A500 GR B—2010, wherein “T” represents the thickness of the crushing tube as manufactured. All the material products were tested for variation in size, mechanical and chemical properties under various thermal conditions. A 0.188″ thickness crushing tube was used as the base sample for comparison purposes. The mill certificate certifies the products to be of the desired good quality and indicates the yield strength of the specific material used for the crushing tube. 
     
       
         
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Tensile  
                 Y.P 
               
               
                   
                 S.N 
                 Heat No. 
                 T 
                 L 
                 (psi) 
                 (psi) 
               
               
                   
                   
               
             
             
               
                   
                 1. 
                 472005537  
                 0.188  
                 40 
                 65,702 
                 46,977 
               
               
                   
                 2. 
                 473005414  
                 0.250  
                 20 
                 67,008 
                 47,853 
               
               
                   
                 3. 
                 473005419 
                 0.250  
                 40 
                 65,267 
                 46,290 
               
               
                   
                 4. 
                 473002067 
                 0.188  
                 20 
                 70,199 
                 57,290 
               
               
                   
                 5. 
                 473002067 
                 0.188  
                 40 
                 70,199 
                 57,290 
               
               
                   
                 6. 
                 473005414  
                 0.250  
                 20 
                 67,008 
                 47,863 
               
               
                   
                   
               
             
          
         
       
     
     Persons skilled in the art will recognize that many modifications and variations are possible in the details, materials, and arrangements of the parts and actions which have been described and illustrated in order to explain the nature of this inventive concept and that such modifications and variations do not depart from the spirit and scope of the teachings and claims contained therein. 
     All patent and non-patent literature cited herein is hereby incorporated by references in its entirety for all purposes.