I declare that the work presented in this thesis entitled "Structural Behavior of Unreinforced and Reinforced Cement Stabilized Soil Columns under Axial Compression" for the award of the degree of Doctor of Philosophy and submitted to the Department of Civil Engineering, Indian Institute i Technology Guwahati, India, is an authentic record of my work. Deb Dulal Tripura at the Indian Institute of Technology Guwahati, India, for the award of the degree of Doctor of Philosophy, is a record of the genuine research work undertaken by him.
Contents
123 7.1.3 Structural behavior of CSRE columns reinforced with steel 124 7.1.4 Structural behavior of CSRE columns reinforced with bamboo steel 125 .
List of Tables
5.9 (a) Axial deformation of columns at end load; and (b) lateral deformation of columns at 60 kN load. 6.10 (a) Load capacity of BSR and SR columns with respect to total reinforcement ratio; and (b) load capacity of BSR and SR columns with respect to lateral reinforcement.
Notations
Pus200 Ultimate load of steel reinforced CSRE column at an anchor spacing of 200 mm. Pubs200 Ultimate load of a steel reinforced CSRE column at an anchor spacing of 200 mm. Xa Average of a test series X1 Lowest result of a test series Xs Standard deviation of a test series.
Introduction
General
Gupta (2014) reported on the effect of using diagonal and horizontal struts on the load capacity of reinforced steel CSRE columns. Additionally, though, studies have shown that bamboo can be a potential substitute for steel in concrete structural elements such as beams and columns (e.g. Ghavami, 2005; Agarwal et al., 2014) and can improve ductility. of the wall struck with soil under horizontal load. (Gao et al., 2009), no reports were found in the literature on the use of bamboo as reinforcement for CSRE columns.
Objectives of the investigation
To evaluate the structural behavior of axially loaded CSRE columns having square, rectangular and circular sections, considering the effects of important parameters such as slenderness ratio, cross-sectional aspect ratio etc., on load deformation, failure patterns etc. To evaluate the structural behavior of axially loaded steel and bamboo steel reinforced CSRE columns with square cross sections, taking into account the effects of structural parameters such as ratio of transverse reinforcement, ratio of total reinforcement, etc., on the failure pattern; load-lateral deformation and load-axial deformation of columns.
Thesis organization
Effects of structural parameters such as total reinforcement ratio, lateral reinforcement ratio, etc., on the failure pattern; load-lateral deformation and load-axial deformation of columns were studied. Effects of structural parameters such as total reinforcement ratio, lateral reinforcement ratio etc., on the failure pattern; load-lateral deformation and load-axial deformation of columns were studied.
Literature Review
- Introduction
- Historical background on rammed earth constructions
- Suitability of soil for rammed earth constructions
- Sustainability of rammed earth constructions
- Structural behaviour of rammed earth walls/columns
- Unreinforced rammed earth
- Codes of practice on rammed earth constructions
- Summary and conclusions
Lindsay (2012) briefly described the use of structural steel elements (steel bars) within stabilized rammed earth walls. The structural behavior of unstabilized and cement-stabilized earthen walls and columns has been studied.
Materials Characterization
Introduction
Therefore, the present chapter studies the properties of locally available soil at Agartala, India and its suitability as a construction material, followed by an attempt to select and validate block-making equipment and technique that can be used for the construction of rammed ground structures. The properties of unstabilized and stabilized (with cement) rammed earth blocks in terms of density, strength and durability are presented.
Experimental programme
- Materials
- Determination of optimum moisture content and maximum dry density The water content at which a specified compactive force can compact a soil mass to
- Equipment for production of rammed earth blocks
- Production of test samples
- Effect of compaction energy
The moisture content of the sun-dried soil was determined with a rapid moisture meter prior to production of rammed soil blocks, ensuring an additional level of standardization. The moisture content of a representative sample of fragments taken from the interior of the tested specimens was determined in accordance with IS 4332 Part 2 (2006a).
Experimental results and discussions
- Density
- Effect of cement content and density on compressive strength
- Effect of age of curing on compressive strength
- Effect of cement content on stress-strain characteristics
- Effect of compaction energy on compressive strength and density
- Durability test
- Effect of cement content on tensile strength
For a given compaction effort, the variations in dry density due to the type of soil-cement ratio are directly related to the characteristic unconfined compressive strength of the specimens in both the hardened and unhardened conditions, as shown in Fig. . However, it can be observed that the increase in compressive strength is ~50% for higher cement content (i.e. 8 and 10%), while it is relatively. Similarly, ITM increases from 0.1 to 2 GPa as compressive strength and cement content increase from 1.1 to 9.73 MPa and 0 to 10%, respectively.
Summary and conclusions
For a given compaction effort, the variations in dry density due to the type of soil-cement ratio are directly related to the characteristic unconfined compressive strength of the CSRE blocks in both hardened and unhardened conditions. At optimal moisture content, it is not possible to achieve the maximum dry density and compressive strength of CSRE blocks, although the compaction energy becomes greater than the standard Proctor effort. The elastic modulus of CSRE blocks is sensitive to variation in compressive strength and cement content, and it is possible to obtain the desired modulus value by adjusting the compressive strength and cement percentage.
Structural Behaviour of CSRE Column
Introduction
Maniatidis and Walker (2008) first attempted to validate the use of masonry design rules for the design of unstabilized square columns with packed soil. However, their study did not explicitly explain the stress reduction factors for concentric axially loaded columns. Therefore, there is a need for further validation of masonry design rules taking into account structural parameters such as slenderness ratio (λ = height (h) / thickness (d) ratio), aspect ratio (Ф = width (a) / thickness (d) ratio) etc. ., to factors for reducing the bearing capacity of axially loaded columns.
Experimental programme
- Materials
- Equipments used for production of test specimen
The upper part of the pipe was left with 400 mm of extra height of each column to facilitate the placement of the rammer in the mold (or act as a collar). The inner walls of the mold were covered/glued with either thin polyethylene or cello tape to avoid adhesion of the test sample to the mold walls. Moreover, the lateral movement at the top of the column in the direction perpendicular to the plane was limited by the loading system.
Results and discussion
- Strength and failure pattern of prisms and cylinders
- Failure patterns of column
- Moisture content and density of column
- Strength and design of column
- Comparison of capacity reduction factors (k)
- Characteristic strength of column
This shows that the deformation of the column increases with increasing values of λ (see Table 4.3). It is interesting to note that although the values of Pu are of the order S <. However, the predictions made by BS 5628 Part 1 (1992) can be considered relatively higher even after consideration of experimental variations.
Summary and conclusions
62 in the case of circular columns, apart from the formation of vertical split cracks with an equal inclination (~ 120°) due to the 'axe action' of the shear wedge. However, in the case of circular columns, the code values are higher by about ∼7%, thus indicating relatively non-conservative. Typical circular column Typical circular column. a) Schematic diagram of the test setup. a) Schematic diagram of the test setup.
Structural Behaviour of Steel Reinforced CSRE Column
Introduction
80 structural parameters such as lateral reinforcement ratio, total reinforcement ratio, etc., on load capacity, deformation, failure patterns, etc. Therefore, in the present chapter, an attempt has been made to study the behavior of steel-reinforced CSRE columns under axial compression, taking into account the effects of the above structural parameters.
Materials and equipments used for production of test specimen
- Soil
- Cement
- Steel
- Equipments and techniques
- Production of test specimen
- Column test
This plate was inserted into the mold by piercing the steel bars through the perforations, which allowed the bars to be positioned vertically and the soil-cement mixture (soaked mixture) compacted evenly. The steel bars tied in the four corners of the steel ties were placed upright inside the mould, followed by pouring/loading the required amount of wet mix and leveling (Figure 5.3a). The perforated steel plate was then placed on top of the moistened mixture so that the steel rods passed through the four holes of the plate.
Results and discussions
- Failure and load-deformation response of column
- Moisture content and density of column
Peeling of cover occurred near the center of the column where the maximum deformation occurred followed by bending of steel bars leading to ultimate failure. This led to a relatively smoother curvature of the failure zone in SR50 (see Fig. 5.7a), and this can be attributed to the improved distributed stress with increased confinement effect, with decreasing bond spacing (i.e., it can thus be seen that the overall response of Pus/Pu of the column with confinement effect of the steel reinforcement appears to follow a non-linear S-curve (i.e. a double curvature curve) that plateaus at both ends.
Summary and conclusions
Therefore, the moisture content of the CSRE was determined to evaluate its effect on the strength and behavior of the column specimen. 88 of the column can be used as a structural part for the construction of low-rise houses rammed into the ground. Steel can be a potential reinforcing material in CSRE columns with narrow joint spacing to achieve higher strength and better seismic performance.
Structural Behaviour of Bamboo-Steel Reinforced CSRE Column
Introduction
101 splints replacing the longitudinal steel bars in CSRE columns under axial loading (see the previous chapter for steel-reinforced CSRE columns), taking into account the effects of structural parameters such as the total reinforcement ratio, the lateral reinforcement ratio, etc.
Materials and equipments used for production of test specimen
- Soil
- Cement
- Bamboo
- Steel
- Equipments and techniques
- Production of test specimen
- Column test
The size of the columns used in the bamboo steel-reinforced column trial program was chosen to be the same (150 mm x 150 mm x 1500 mm) as the steel-reinforced columns presented in Chapter 5. The dimensions of the columns were the same to facilitate the comparison of structural properties between bamboo steel and steel-reinforced columns. Bamboo steel reinforced (BSR; bamboo as longitudinal reinforcement and steel as lateral reinforcement) are then designated as BSR200, BSR100 and BSR50 depending on tie spacing, where BSR200 denotes a column with 200mm tie center spacing.
Results and discussions
- Failure and load-deformation response of column .1 Effect of 200 mm tie spacing
- Effect of reinforcement on load-capacity
- Comparison of BSR and SR columns
The subsequent loading resulted in complete failure of the cover at mid-height of the column due to bending followed by the fracture of the bamboo struts. A tensile crack is visible on the tension side, and the cover is crushed on the pressure side. The failure pattern of columns with smaller bond spacing such as BSR50 (i.e. 33.3% of the column width) is shown in Fig.
Summary and conclusions
It can be seen that the values of δuv and δl60 for SR turn out to be higher than the values for BSR by ~8% and ~16% respectively for larger bond distance, i.e. structural behavior of bamboo-steel reinforced CSRE column. a) mold; (b) rammer and compaction plate with hollow steel reinforced CSRE column. Failure of column with lateral deformation curve. bracket Spalling of cover due to compression crushing.
Conclusions and Future Scope of Work
Introduction
- Characteristics properties of CSRE blocks
- Structural Behaviour of CSRE columns of circular, square and rectangular sections
- Structural behaviour of steel reinforced CSRE columns
- Structural behaviour of bamboo-steel reinforced CSRE column
The load capacity also increases by about 11% to 30% when the percentage of transverse reinforcement ratio is increased from 0.63% to 1.26% and 2.51% respectively. Load capacity (ultimate load for bamboo-steel-reinforced column) of bamboo-reinforced CSRE columns is about 3.7% to 15% higher than that of unreinforced CSRE column when the total (bamboo and steel) reinforcement ratio of 1.52% be increased to 3.41%. Linear increase in percentage load capacity is observed as total reinforcement is increased from 0% to 3.41%.
Future scope of work
Therefore, steel can be a potential reinforcement material in CSRE columns with closer bond spacing to achieve higher strength and better seismic performance. Similar failure patterns as for steel-reinforced CSRE columns are observed for bamboo steel-reinforced CSRE columns, except for post-ultimate snapping or fracture of bent bamboo longitudinal reinforcement. A further study needs to be carried out on CSRE columns to derive stress reduction factors useful for design calculations.
The effect of moisture content on the mechanical properties of compacted soil.” Construction and building materials. Joint behavior of bamboo struts in cement stabilized rammed earth blocks. International Journal of Sustainable Engineering. Pull-out test on deformed and flat reinforcement in cement-stabilized compacted soil.” Journal of Materials in Construction.
Appendix A
Compaction energy calculation for standard Proctor test
Compaction energy calculation for wooden cubic mould
Appendix B
- Determination of tangent modulus for columns from the stress- strain curve of prism
- Determination of stress/capacity reduction factor
- Determination of factor of safety
- Lateral reinforcement
The tangent modulus (Et) of the S-0.9 column is determined by finding the slope of the tangent, i.e., 155. The stress reduction or capacity factor (k) is determined by dividing the average compressive strength or load capacity of the corresponding column series by the average compressive strength or load capacity of the slenderness ratio of the series of columns equal to 6. B.3 Determination of the safety factor. A = cross-sectional area of CSRE core bounded by centerline of outer bond s = center-to-center spacing between bonds. c = lateral dimension of the CSRE core.
List of Publications Journal
Conference
