Constraints Files

Once the required reinforcement is calculated, the physical reinforcement elements have to be designed in such a way that it satisfies optimally the design constraints, code specifications, and other particular demands. Usually, the engineer has to evaluate all the possibilities based on his own experience and knowledge in order to determinate the most convenient solution.

One approach to access such kind of implicitly given knowledge is Expert System technology. Expert systems are regarded as branch in the area of Artificial Intelligence and are currently used in many fields of application like medical diagnostics or assembly layout of computers. One of the key assumptions in (rule based) expert systems is, that the knowledge of an expert can be expressed in IF … THEN … type rules. The system provides facilities to enter these rules by the expert in a very simple and accessible syntax, often similar to human language, which enables the expert to enter his knowledge without deeper programming skills. These rules are then processed by the expert system within the so-called inference engine in order to generate new conclusions or initiate certain actions.

The automatic generation of the 3D-rebar model in SOFiSTiK Reinforcement Generation follows this approach. Each step in the generation of the rebar model, like the determination of the rebar layout in the cross-section or the calculation of anchorage and laps can be controlled by rules.

For example, in order to control the diameter of the longitudinal bars in a beam, the user may define the following rules:

//$ range of allowed parameters for the diameter of longitudinal bars.
d_asl = [ 0.006, 0.008, 0.010, 0.012, 0.014, 0.016, 0.020, 0.025, 0.028, 0.032, 0.040 ]

//$ restrictions of the range according to the height of the cross-section
Is_Beam {
  d_asl <= 0.028
  Section_Height <= 0.50 : d_asl <= 0.025
  Section_Height <= 0.40 : d_asl <= 0.025
  Section_Height >= 0.50 : d_asl >= 0.016
  Section_Height >= 0.80 : d_asl >= 0.020
}

According to the different requirements in the design process, there will also be different kind of rule sets for controlling the rebar generation. There will be rules for maintaining the design code regulations or rules which the user can define on a project or company specific basis.

Optimization

The definition of the physical reinforcement can be controlled by the engineer in order to optimize the automatic generation of the 3D rebar model and produce an outcome that satisfies several objectives.

The requirements of the engineer are captured by means of weighting factors which act on particular goals, increasing or decreasing their relevance during the generation process.

These factors are stored in the constraints file:

//$ weighting factors ( >1.0 increases effect, <1.0 decreases effect, 0.0 no effect)
//$ F1: try to use as less bars as possible (increase rather diameter than number)
//$ F2: try to reduce difference between inserted and required reinforcement
//$ F3: try to avoid using multiple layers of reinforcement (bending beams only)
//$ F4: prefer to use same diameter for base and supplemental reinforcement
//$ F5-F8: reserved
W_FACTORS = [ 1.0, 1.0, 1.0, 0.0, 1.0, 1.0, 1.0, 1.0 ]

Parameters

Definitions of predefined parameters which can be used in a constraints file in order to create or modify design rules are listed in the following.

Note

The parameter’s input is not case sensitive.

Material Properties

F_CD	Design compressive strength of concrete [MPa]
F_CK	Nominal strength of concrete [MPa]
F_CM	Mean value of compressive strength of concrete [MPa]
F_CTD	Design tensile strength of concrete [MPa]
F_CTM	Mean value of tensile strength of concrete [MPa]
F_BD	Bond strength of concrete [MPa] (DIN EN1992-1-1, 8.4.2)
F_YK	Characteristic yield strength of reinforcement [MPa]
F_YD	Design yield strength of reinforcement [MPa]
F_TK	Characteristic tensile strength of reinforcement [MPa]

Section & Layer Geometry

SECTION_HEIGHT	Height of section [m]
SECTION_WIDTH	Width of section [m]
LAYER_ID	Number of layer
LAYER_ZS	Local z-coordinate of layer [m]
LAYER_WIDTH	Length of layer [m]
IS_COLUMN	Boolean variable: 1=true, 0=false
IS_BEAM	Boolean variable: 1=true, 0=false
ISLOWERREINFORCEMENT	Boolean variable: 1=true, 0=false
ISUPPERREINFORCEMENT	Boolean variable: 1=true, 0=false
ISBASEREINFORCEMENT	Boolean variable: 1=true, 0=false
MAXBARSTEPDIFFERENCE	Maximum step difference between base and supplemental reinforcement diameter

Longitudinal Reinforcement

ISMAINDIRECTION	Condition for reinforcement in main direction (Boolean variable: 1=true, 0=false)
C_ASL	Cover of longitudinal reinforcement [m]
D_ASL	Diameter of longitudinal reinforcement used [m]
D_KST	Diameter of constructive reinforcement [m]
D_ASL	Diameter of base longitudinal reinforcement [m]
D_ASL2	Diameter of supplemental longitudinal reinforcement [m]
S_ASL	Spacing of longitudinal reinforcement [m]
S_ASL2	Spacing of longitudinal reinforcement [m]
ASL_REQ_MAX	Required maximal longitudinal reinforcement [m2]
ASL_PRO	Longitudinal reinforcement provided [m2]
N_ASL	Number of longitudinal bars
ASL_UTIL	Utilization factor as_req/as_pro
F_ASL	Factor for over-/under-reinforcement

Shear / Transverse Reinforcement

ISTRANSDIRECTION	Condition for reinforcement in transverse direction (Boolean variable: 1=true, 0=false)
C_ST	Cover of shear reinforcement [m]
D_ST	Diameter of shear reinforcement [m]
S_ST	Spacing of shear reinforcement [m]
ASB_REQ_MAX	Required shear reinforcement [m2/m]
ASB_PRO	Minimum shear reinforcement [m2/m]
HOOK_ANGLE	Angle of the hook
HOOK_LENGTH	Length of the hook
F_ASB	Factor for over-/under-reinforcement

Anchorage of Reinforcement

IS_ANCHORAGE_STRAIGHT	Boolean variable: 1=true, 0=false
IS_ANCHORAGE_BEND_BAR	Boolean variable: 1=true, 0=false
IS_ANCHORAGE_HOOK	Boolean variable: 1=true, 0=false
IS_ANCHORAGE_WELDED	Boolean variable: 1=true, 0=false
ALPHA_1	Factor considering shape of bars
ALPHA_2	Factor considering concrete minimum cover
ALPHA_3	Effect of confinement by not welded transverse reinforcement
ALPHA_4	Effect of confinement by welded transverse reinforcement
ALPHA_5	Effect of transverse pressure
ALPHA_6	Percentage of lapped bars (DIN EN1992-1-1, 8.7.3 (2))
LB_RQD	Base value of development length [m] (DIN EN1992-1-1, 8.4.3 (2))
LB_D	Design value of development length [m] (DIN EN1992-1-1, 8.4.4 (1))
LB_EQ	Alternative development length [m] (DIN EN1992-1-1, 8.4.4 (2))
D_MIN	Mandrel diameter for longitudinal bars [m]
D_MINST	Mandrel diameter for strirrups [m]
L_0	Lap length [m]
REINFORCEMENTINTENSION	Boolean variable: 1=true, 0=false
REINFORCEMENTINCOMPRESSION	Boolean variable: 1=true, 0=false
PERCENTAGELAPPEDBARS	Percentage of lapped bars (Table 8.3)
ISBONDGOOD	Boolean variable: 1=true, 0=false

Plates only

IS_FLOOR	Boolean variable: 1=true, 0=false
IS_WALL	Boolean variable: 1=true, 0=false
THICKNESS	Thickness of Slab / wall [m]
SOFLAYERS	Boolean variable: 1=true, 0=false
BASEREINFORCEMENTSYSTEM	Boolean variable: 1=true, 0=false. Area reinforcement will be used for base reinforcement
BAR_LEN	Minimum valid length of rebars [m]
AS_DIFF	Differential As to consider a change in the reinforcement distribution [m2/m]
MERGE_LEN	Maximum length to merge rebar sets [m]
MERGE_AS	As to consider two reinforcement surfaces as able-to-merge [m2/m]
AS_BASE	Base reinforcement [m2/m]
NO_BASE_REINFORCEMENT	Create no base reinforcement, Boolean variable: 1=true, 0=false
RECOGNIZE_REINFORCEMENT	Consider existing reinforcement, Boolean variable: 1=true, 0=false

Other

W_FACTORS	Weighting factors used in optimization
CONSTRAINTSFILE_ONLY	Boolean variable: 1=true, 0=false. Ignore dialog input
CREATESINGLEBARS	Boolean variable: 1=true, 0=false. Create single bars (no rebar sets)
APPLYMATCHINGXFORM	Boolean variable: 1=true, 0=false. Compare exported geometry with Revit geometry to create bars in the Revit location (CDB only)
ADSJUSTTOSECTION	Boolean variable: 1=true, 0=false. Adjust parametrically the reinforcement to the Revit geometry in case it is distinct to the exported model(CDB only)

Anchorage

The determination of anchorage and laps can be controlled by design rules. The anchorage development length is defined by the parameter “LB_D”, the engineer can modify the constraints file and influence on its calculation.

In the default constraint file, the anchorage length in defined according the Eurocode EN 1992-1-1:2004 as follows:

//$ --------------------------------------------------------------------
//$ 8.4 Anchorage of longitudinal reinforcement
//$ --------------------------------------------------------------------

//$ 8.4.2 Ultimate bond stress
f_bd = 2.25*eta_1*eta_2*f_ctd

//$ 8.4.2. Bond conditions
eta_1 = 0.7 ; isBondGood : eta_1 = 1.0
eta_2 = 1.0 ; d_asl > 0.032 : eta_2 = (0.132-d_asl)*10

//$ 8.4.4 Design anchorage length
lb_d = alpha_1*alpha_2*alpha_3*alpha_4*alpha_5 * lb_rqd * asl_util

//$ 8.4.4 (1) Minimum anchorage length
reinforcementInTension     : lb_d >= MAX(0.3*alpha_1*alpha_4*lb_rqd,10*d_asl)
reinforcementInCompression : lb_d >= MAX(0.6*lb_rqd,10*d_asl)

//$ 8.4.4 (2) alternative anchorage length
lb_eq = 0.7 * lb_rqd * asl_util

//$ Coefficients of Table 8.2
alpha_1 = 1.0 //$ factor considering shape of bars
alpha_2 = 1.0 //$ factor considering concrete minimum cover
alpha_3 = 1.0 //$ effect of confinement by not welded transverse reinforcement
alpha_4 = 1.0 //$ effect of confinement by welded transverse reinforcement
alpha_5 = 1.0 //$ effect of transverse pressure

The anchorage length is considered for the visualization of the reinforcement as an offset on the inserted reinforcement range measured since the beginning/end of the bars. Below the anchorage length is highlighted green next to the boundary of the reinforcement distribution diagram.